Method of minimizing absorption of visible light in infrared dyes

ABSTRACT

The present invention provides a method of minimizing absorption of visible light in an IR-absorbing dye comprising reducing intermolecular interactions between adjacent dye molecules. The method is particularly suitable for use in connection with netpage and Hyperlabel systems.

FIELD OF THE INVENTION

The present application relates to a method of minimizing absorption ofvisible light in infrared (IR) dyes. It has been developed primarily toavoid undesirable coloration in IR inks and, more particularly, to avoidundesirable coloration of substrates printed or marked with IR inks.

CO-PENDING APPLICATIONS

Various methods, systems and apparatus relating to the present inventionare disclosed in the following co-pending applications filed by theapplicant or assignee of the present invention simultaneously with thepresent application: IRB002US IRB003US IRB004US IRB005US IRB006USIRB007US IRB008US IRB009US IRB010US

The disclosures of these co-pending applications are incorporated hereinby cross-reference. Each application is temporarily identified by itsdocket number. This will be replaced by the corresponding USSN whenavailable.

BACKGROUND OF THE INVENTION

IR absorbing dyes have numerous applications, such as optical recordingsystems, thermal writing displays, laser filters, infrared photography,medical applications and printing. Typically, it is desirable for thedyes used in these applications to have strong absorption in the near-IRat the emission wavelengths of semiconductor lasers (e.g. between about700 and 2000 nm, preferably between about 700 and 1000 nm). In opticalrecording technology, for example, gallium aluminium arsenide (GaAlAs)and indium phosphide (InP) diode lasers are widely used as lightsources.

Another important application of IR dyes is in inks, such as printinginks. The storage and retrieval of digital information in printed formis particularly important. A familiar example of this technology is theuse of printed, scannable bar codes. Bar codes are typically printedonto tags or labels associated with a particular product and containinformation about the product, such as its identity, price etc. Barcodes are usually printed in lines of visible black ink, and detectedusing visible light from a scanner. The scanner typically comprises anLED or laser (e.g. a HeNe laser, which emits light at 633 nm) lightsource and a photocell for detecting reflected light. Black dyessuitable for use in barcode inks are described in, for example,WO03/074613.

However, in other applications of this technology (e.g. securitytagging) it is desirable to have a barcode, or other intelligiblemarking, printed with an ink that is invisible to the unaided eye, butwhich can be detected under UV or IR light.

An especially important application of detectable invisible ink is inautomatic identification systems, and especially “netpage™” and“Hyperlabel™” systems. Netpage systems are described in the followingpatent applications, all of which are incorporated herein by reference.

CROSS-REFERENCES

Various methods, systems and apparatus relating to the present inventionare disclosed in the following co-pending applications filed by theapplicant or assignee of the present application: 10/409,876 10/409,84810/409,845 09/575,197 09/575,195 09/575,159 09/575,132 09/575,12309/575,148 09/575,130 09/575,165 09/575,153 09/693,415 09/575,11809/609,139 09/608,970 09/575,116 09/575,144 09/575,139 09/575,18609/575,185 09/609,039 09/663,579 09/663,599 09/607,852 09/575,19109/693,219 09/575,145 09/607,656 09/693,280 09/609/132 09/693,51509/663,701 09/575,192 09/663,640 09/609,303 09/610,095 09/609,59609/693,705 09/693,647 09/721,895 09/721,894 09/607,843 09/693,69009/607,605 09/608,178 09/609,553 09/609,233 09/609,149 09/608,02209/575,181 09/722,174 09/721,896 10/291,522 10/291,517 10/291,52310/291,471 10/291,470 10/291,819 10/291,481 10/291,509 10/291,82510/291,519 10/291,575 10/291,557 10/291,661 10/291,558 10/291,58710/291,818 10/291,576 10/291,589 10/291,526 6,644,545 6,609,6536,651,879 10/291,555 10/291,510 19/291,592 10/291,542 10/291,82010/291,516 10/291,363 10/291,487 10/291,520 10/291,521 10/291,55610/291,821 10/291,525 10/291,586 10/291,822 10/291,524 10/291,55310/291,511 10/291,585 10/291,374 10/685,523 10/685,583 10/685,45510/685,584 10/757,600 09/575,193 09/575,156 09/609,232 09/607,84409/607,657 09/693,593 10/743,671 09/928,055 09/927,684 09/928,10809/927,685 09/927,809 09/575,183 09/575,160 09/575,150 09/575,1696,644,642 6,502,614 6,622,999 09/575,149 10/322,450 6,549,935 NPN004US09/575,187 09/575,155 6,591,884 6,439,706 09/575,196 09/575,19809/722,148 09/722,146 09/721,861 6,290,349 6,428,155 09/575,14609/608,920 09/721,892 09/722,171 09/721,858 09/722,142 10/171,98710/202,021 10/291,724 10/291,512 10/291,554 10/659,027 10/659,02609/693,301 09/575,174 09/575,163 09/693,216 09/693,341 09/693,47309/722,087 09/722,141 09/722,175 09/722,147 09/575,168 09/722,17209/693,514 09/721,893 09/722,088 10/291,578 10/291,823 10/291,56010/291,366 10/291,503 10/291,469 10/274,817 09/575,154 09/575,12909/575,124 09/575,188 09/721,862 10/120,441 10/291,577 10/291,71810/291,719 10/291,543 10/291,494 10/292,608 10/291,715 10/291,55910/291,660 10/409,864 10/309,358 10/410,484 10/683,151 10/683,04009/575,189 09/575,162 09/575,172 09/575,170 09/575,171 09/575,16110/291,716 10/291,547 10/291,538 10/291,717 10/291,827 10/291,54810/291,714 10/291,544 10/291,541 10/291,584 10/291,579 10/291,82410/291,713 10/291,545 10/291,546 09/693,388 09/693,704 09/693,51009/693,336 09/693,335 10/181,496 10/274,119 10/309,185 10/309,066NPW014US NPS047US NPS048US NPS049US NPS050US NPS051US NPS052US NPS053USNPS054US NPS045US NPS046US NPT037US NPA138US NPA136US HYC001US HYC002USHYC003US HYC004US HYC005US HYC006US HYC007US HYC008US HYC009US HYC010USHYC011US HYD001US HYG001US HYG002US HYG003US HYG004US HYG005US HYG006USHYG007US HYG008US HYG009US HYGO10US HYG011US HYG012US HYG013US HYG014USHYG015US HYG016US HYJ001US HYJ002US HYT001US HYT002US HYT003US HYT004USHYT005US HYT006US HYT007US HYT008US IRA001US IRA002US IRA003US NPA148USNPP038US NPS059US NPA141US NPT039US NPT025US

The disclosures of all of these co-pending patents/patent applicationsare incorporated herein by reference. Some patent applications aretemporarily identified by their docket number. This will be replaced bythe corresponding application number when available.

In general, the netpage system relies on the production of, and humaninteraction with, netpages. These are pages of text, graphics and imagesprinted on ordinary paper, but which work like interactive web pages.Information is encoded on each page using ink which is substantiallyinvisible to the unaided human eye. The ink, however, and thereby thecoded data, can be sensed by an optically imaging pen and transmitted tothe netpage system.

Active buttons and hyperlinks on each page may be clicked with the pento request information from the network or to signal preferences to anetwork server. In some forms, text written by hand on a netpage may beautomatically recognized and converted to computer text in the netpagesystem, allowing forms to be filled in. In other forms, signaturesrecorded on a netpage may be automatically verified, allowing e-commercetransactions to be securely authorized.

Netpages are the foundation on which a netpage network is built. Theymay provide a paper-based user interface to published information andinteractive services.

A netpage consists of a printed page (or other surface region) invisiblytagged with references to an online description of the page. The onlinepage description is maintained persistently by a netpage page server.The page description describes the visible layout and content of thepage, including text, graphics and images. It also describes the inputelements on the page, including buttons, hyperlinks, and input fields. Anetpage allows markings made with a netpage pen on its surface to besimultaneously captured and processed by the netpage system.

Multiple netpages can share the same page description. However, to allowinput through otherwise identical pages to be distinguished, eachnetpage is assigned a unique page identifier. This page ID hassufficient precision to distinguish between a very large number ofnetpages.

Each reference to the page description is encoded in a printed tag. Thetag identifies the unique page on which it appears, and therebyindirectly identifies the page description. The tag also identifies itsown position on the page.

Tags are printed in infrared-absorptive ink on any substrate which isinfrared-reflective, such as ordinary paper. Near-infrared wavelengthsare invisible to the human eye but are easily sensed by a solid-stateimage sensor with an appropriate filter.

A tag is sensed by an area image sensor in the netpage pen, and the tagdata is transmitted to the netpage system via the nearest netpageprinter. The pen is wireless and communicates with the netpage printervia a short-range radio link. Tags are sufficiently small and denselyarranged that the pen can reliably image at least one tag even on asingle click on the page. It is important that the pen recognize thepage ID and position on every interaction with the page, since theinteraction is stateless. Tags are error-correctably encoded to makethem partially tolerant to surface damage.

The netpage page server maintains a unique page instance for eachprinted netpage, allowing it to maintain a distinct set of user-suppliedvalues for input fields in the page description for each printednetpage.

Hyperlabel™ is a trade mark of Silverbrook Research Pty Ltd, Australia.In general, Hyperlabel™ systems use an invisible (e.g. infrared) taggingscheme to uniquely identify a product item. This has the significantadvantage that it allows the entire surface of a product to be tagged,or a significant portion thereof, without impinging on the graphicdesign of the product's packaging or labeling. If the entire surface ofa product is tagged (“omnitagged”), then the orientation of the productdoes not affect its ability to be scanned i.e. a significant part of theline-of-sight disadvantage of visible barcodes is eliminated.Furthermore, if the tags are compact and massively replicated(“omnitags”), then label damage no longer prevents scanning.

Thus, hyperlabelling consists of covering a large portion of the surfaceof a product with optically-readable invisible tags. When the tagsutilize reflection or absorption in the infrared spectrum, they arereferred to as infrared identification (IRID) tags. Each Hyperlabel™ taguniquely identifies the product on which it appears. The tag maydirectly encode the product code of the item, or it may encode asurrogate ID which in turn identifies the product code via a databaselookup. Each tag also optionally identifies its own position on thesurface of the product item, to provide the downstream consumer benefitsof netpage interactivity.

Hyperlabels™ are applied during product manufacture and/or packagingusing digital printers, preferably inkjet printers. These may be add-oninfrared printers, which print the tags after the text and graphics havebeen printed by other means, or integrated colour and infrared printerswhich print the tags, text and graphics simultaneously.

Hyperlabels™ can be detected using similar technology to barcodes,except using a light source having an appropriate near-IR frequency. Thelight source may be a laser (e.g. a GaAlAs laser, which emits light at830 nm) or it may be an LED.

From the foregoing, it will be readily apparent that invisible IRdetectable inks are an important component of netpage and Hyperlabel™systems. In order for an IR absorbing ink to function satisfactorily inthese systems, it should ideally meet a number of criteria:

-   -   (i) compatibility with inkjet printers;    -   (ii) compatibility of the IR dye with aqueous solvents used in        inkjet inks;    -   (iii) intense absorption in the near infra-red region (e.g. 700        to 1000 nm);    -   (iv) zero or low intensity visible absorption;    -   (v) lightfastness;    -   (vi) thermal stability;    -   (vii) zero or low toxicity;    -   (viii) low-cost manufacture;    -   (ix) adheres well to paper and other media; and    -   (x) no strikethrough and minimal bleeding of the ink on        printing.

Hence, it would be desirable to develop IR dyes and ink compositionsfulfilling at least some and preferably all of the above criteria. Suchinks are desirable to complement netpage and Hyperlabel™ systems.

Some IR dyes are commercially available from various sources, such asEpolin Products, Avecia Inks and H.W. Sands Corp.

In addition, the prior art describes various IR dyes. U.S. Pat. No.5,460,646, for example, describes an infrared printing ink comprising acolorant, a vehicle and a solvent, wherein the colorant is a silicon(IV) 2,3-naphthalocyanine bis-trialkylsilyloxide.

U.S. Pat. No. 5,282,894 describes a solvent-based printing inkcomprising a metal-free phthalocyanine, a complexed phthalocyanine, ametal-free naphthalocyanine, a complexed naphthalocyanine, a nickeldithiolene, an aminium compound, a methine compound or an azulenesquaricacid.

However, none of the prior art dyes can be formulated into inkcompositions suitable for use in netpage or Hyperlabel™ systems. Inparticular, commercially available and/or prior art inks suffer from oneor more of the following problems: absorption at wavelengths unsuitablefor detection by near-IR sensors; poor solubility or dispersibility inaqueous solvent systems; or unacceptably high absorption in the visiblepart of the spectrum.

In a typical netpage, there may be a large number of hyperlinks on onepage and correspondingly relatively large areas of the page printed withIR ink. In the Hyperlabel™ system, the majority of a product's packagingmay be printed with the invisible ink. Thus, it is especially desirablethat the ink used is invisible to the unaided eye and contains minimalresidual colour.

Moreover, inkjet printing is the preferred means for generating netpagesand Hyperlabels™. Inkjet printing is preferred primarily for itshigh-speed and low cost. Inkjet inks are typically water-based forreasons of low cost, low toxicity and low flammability. In thermalbubble-jet printers, the ink needs to be rapidly vaporized during theprinting process. This rapid vaporization of the ink during the printingprocess necessitates a water-based ink composition. Accordingly, it isdesirable that the IR dyes used in netpage and Hyperlabel™ inks aresuitable for formulating into aqueous ink compositions and arecompatible with inkjet printers.

A further essential requirement of IR dyes used in netpage systems isthat they must absorb IR radiation at a frequency complementary to thefrequency of the IR sensor in the netpage pen. Preferably, the inkshould contain a dye, which absorbs strongly at the frequency of the IRsensor. Accordingly, the dyes used in netpage systems should absorbstrongly in the near-IR region—that is, 700 to 1000 nm, preferably 750to 900 mm, more preferably 780 to 850 nm.

SUMMARY OF THE INVENTION

In a first aspect, the present invention provides a method of minimizingabsorption of visible light in an IR-absorbing dye, said methodcomprising reducing intermolecular interactions between adjacent dyemolecules.

In a second aspect, the present invention provides a method ofminimizing absorption of visible light in an inkjet ink comprising anIR-absorbing dye, said method comprising reducing intermolecularinteractions between adjacent dye molecules.

In a third aspect, the present invention provides a method of minimizingvisible coloration of a substrate having an IR-absorbing dye disposedthereon, said method comprising reducing intermolecular interactionsbetween adjacent dye molecules.

In a fourth aspect, there is provided a method of enabling entry of datainto a computer system via a printed form, the form containinghuman-readable information and machine-readable coded data, the codeddata being indicative of an identity of the form and of a plurality ofreference points of the form, the method including the steps of:

-   -   receiving, in the computer system and from a sensing device,        indicating data regarding the identity of the form and a        position of the sensing device relative to the form, the sensing        device, when placed in an operative position relative to the        form, generating the indicating data using at least some of the        coded data;    -   identifying, in the computer system and from the indicating        data, at least one field of the form; and    -   interpreting, in the computer system, at least some of the        indicating data as it relates to the at least one field,        wherein said coded data comprises an IR-absorbing dye in which        visible absorption is minimized by a method as described above.

In a fifth aspect, there is provided a method of enabling entry of datainto a computer system via a printed form, the form containinghuman-readable information and machine-readable coded data, the codeddata being indicative of at least one field of the form, the methodincluding the steps of:

-   -   receiving, in the computer system and from a sensing device,        indicating data regarding the at least one field and including        movement data regarding movement of the sensing device relative        to the form, the sensing device, when moved relative to the        form, generating the data regarding said at least one field        using at least some of the coded data and generating the data        regarding its own movement relative to the form; and    -   interpreting, in the computer system, at least some of said        indicating data as it relates to said at least one field,        wherein said coded data comprises an IR-absorbing dye in which        visible absorption is minimized by a method as described above.

In an sixth aspect, there is provided a method of enabling entry of datainto a computer system via a product item, the product item having aprinted surface containing human-readable information andmachine-readable coded data, the coded data being indicative of anidentity of the product item, the method including the steps of:

-   (a) receiving, in the computer system and from a sensing device,    indicating data regarding the identity of the product item, the    sensing device, when placed in an operative position relative to the    product item, generating the indicating data using at least some of    the coded data; and-   (b) recording, in the computer system and using the indicating data,    information relating to the product item,    wherein said coded data comprises an IR-absorbing dye in which    visible absorption is minimized by a method as described above.

In a seventh aspect, there is provided a method of enabling retrieval ofdata from a computer system via a product item, the product item havinga printed surface containing human-readable information andmachine-readable coded data, the coded data being indicative of anidentity of the product item, the method including the steps of:

-   (a) receiving, in the computer system and from a sensing device,    indicating data regarding the identity of the product item, the    sensing device, when placed in an operative position relative to the    product item, generating the indicating data using at least some of    the coded data;-   (b) retrieving, in the computer system and using the indicating    data, information relating to the product item; and-   (c) outputting, from the computer system and to an output device,    the information relating to the product item, the output device    selected from the group comprising a display device and a printing    device,    wherein said coded data comprises an IR-absorbing dye in which    visible absorption is minimized by a method as described above.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a schematic of a the relationship between a sample printednetpage and its online page description;

FIG. 2 is a schematic view of a interaction between a netpage pen, a Webterminal, a netpage printer, a netpage relay, a netpage page server, anda netpage application server, and a Web server;

FIG. 3 illustrates a collection of netpage servers, Web terminals,printers and relays interconnected via a network;

FIG. 4 is a schematic view of a high-level structure of a printednetpage and its online page description;

FIG. 5 a is a plan view showing the interleaving and rotation of thesymbols of four codewords of the tag;

FIG. 5 b is a plan view showing a macrodot layout for the tag shown inFIG. 5 a;

FIG. 5 c is a plan view showing an arrangement of nine of the tags shownin FIGS. 5 a and 5 b, in which targets are shared between adjacent tags;

FIG. 5 d is a plan view showing a relationship between a set of the tagsshown in FIG. 5 a and a field of view of a netpage sensing device in theform of a netpage pen;

FIG. 6 is a perspective view of a netpage pen and its associatedtag-sensing field-of-view cone;

FIG. 7 is a perspective exploded view of the netpage pen shown in FIG.6;

FIG. 8 is a schematic block diagram of a pen controller for the netpagepen shown in FIGS. 6 and 7;

FIG. 9 is a perspective view of a wall-mounted netpage printer;

FIG. 10 is a section through the length of the netpage printer of FIG.9;

FIG. 10 a is an enlarged portion of FIG. 10 showing a section of theduplexed print engines and glue wheel assembly;

FIG. 11 is a detailed view of the ink cartridge, ink, air and gluepaths, and print engines of the netpage printer of FIGS. 9 and 10;

FIG. 12 is an exploded view of an ink cartridge;

FIG. 13 is a schematic view of the structure of an item ID;

FIG. 14 is a schematic view of the structure of an omnitag;

FIG. 15 is a schematic view of a pen class diagram;

FIG. 16 is a schematic view of the interaction between a product item, afixed product scanner, a hand-held product scanner, a scanner relay, aproduct server, and a product application server;

FIG. 17 is a perspective view of a bi-lithic printhead;

FIG. 18 an exploded perspective view of the bi-lithic printhead of FIG.17;

FIG. 19 is a sectional view through one end of the bi-lithic printheadof FIG. 17;

FIG. 20 is a longitudinal sectional view through the bi-lithic printheadof FIG. 17;

FIGS. 21(a) to 21(d) show a side elevation, plan view, opposite sideelevation and reverse plan view, respectively, of the bi-lithicprinthead of FIG. 17;

FIGS. 22(a) to 22(c) show the basic operational principles of a thermalbend actuator;

FIG. 23 shows a three dimensional view of a single ink jet nozzlearrangement constructed in accordance with FIG. 22;

FIG. 24 shows an array of the nozzle arrangements shown in FIG. 23;

FIG. 25 is a schematic cross-sectional view through an ink chamber of aunit cell of a bubble forming heater element actuator;

FIG. 26 shows an absorption spectrum of a dye prepared according toExample 1;

FIG. 27 shows an absorption spectrum of a dye prepared according toExample 2;

FIG. 28 shows an absorption spectrum of a dye prepared according toExample 3;

FIG. 29 (1 a-d) show reflectance spectra of ink solutions comprisingsulfonated Vanadyl octabutoxyphthalocyanine on plain paper (80 gsm);

FIG. 30 shows an absorption spectrum of a dye prepared according toExample 4;

FIG. 31 shows an absorption spectrum of a dye prepared according toExample 5;

FIG. 32 shows an absorption spectrum of a dye prepared according toExample 6.

DETAILED DESCRIPTION

IR-Absorbing Dye

As used herein, the term “IR-absorbing dye” means a dye substance, whichabsorbs infrared radiation and which is therefore suitable for detectionby an infrared sensor. Preferably, the IR-absorbing dye absorbs in thenear infrared region, and preferably has a λ_(max) in the range of 700to 1000 nm, more preferably 750 to 900 nm, more preferably 780 to 850nm. Dyes having a λ_(max) in this range are particularly suitable fordetection by semiconductor lasers, such as a gallium aluminium arsenidediode laser.

It has been recognized by the present inventors that IR-absorbing dyecompounds of the prior art absorb, at least to some extent, in thevisible region of the spectrum. Indeed, the vast majority ofIR-absorbing dye compounds known in the prior art are black. Thisvisible absorption is clearly undesirable in “invisible” IR inks,especially IR inks for use in netpage or Hyperlabel™ systems.

It has further been recognized by the present inventors that thepresence of visible bands in the IR spectra of IR-absorbing dyecompounds, and particularly IR-absorbing metal-ligand complexes, ismainly due to intermolecular interactions between adjacent molecules.

Typically, IR-absorbing compounds comprise a π-system which forms asubstantially planar moiety in at least part of the molecule. There is anatural tendency for planar π-systems in adjacent molecules to stack ontop of each other via intermolecular π-interactions, known as π-πstacking. Hence, IR-absorbing compounds have a natural tendency to grouptogether via intermolecular π-interactions, producing relatively weaklybound dimers, trimers etc. Without wishing to be bound by theory, it isunderstood by the present inventors that π-π stacking of IR-absorbingcompounds contributes significantly to the production of visibleabsorption bands in their IR spectra, which would not otherwise bepresent in the corresponding monomeric compounds. This visibleabsorption is understood to be due to broadening of IR absorption bandswhen π-systems stack on top of each other and π-orbitals interact,producing small changes in their respective energy levels. Broadening ofIR absorption bands is undesirable in two respects: firstly, it reducesthe intensity of absorption in the IR region; secondly, the IRabsorption band tends to tail into the visible region, producing highlycoloured compounds.

Furthermore, the formation of coloured dimers, trimers etc. via π-πinteractions occurs both in the solid state and in solution. However, itis a particular problem in the solid state, where there are no solventmolecules to disrupt the formation of extended π-stacked oligomers. IRdyes having acceptable solution characteristics may still be intenselycoloured solids when printed onto paper. The ideal “invisible” IR dyeshould remain invisible when the solvent has evaporated or wicked intothe paper.

Additionally, the interaction of π-orbitals with local charges orpartially charged atoms, such as ions, can be large and this mayintroduce additional absorption in the visible region.

None of the prior art addresses the problem visible absorption in IRinks by designing and synthesizing dye molecules specifically adapted toreduce intermolecular interactions in the form of π-π stacking.

Specific examples of moieties suitable for reducing intermolecularinteractions are described in more detail below. However, it will beappreciated from the above that any moiety or group that can interferesufficiently with the intermolecular π-π interactions of adjacent dyemolecules will be suitable for minimizing visible absorption, and willtherefore be suitable for use in the present invention.

Preferably, the moiety configured to reduce intermolecular interactionsreduces these interactions by a steric repulsive effect. Hence, byproviding a dye molecule having suitably positioned sterically repulsivegroup(s), it is possible to increase the distance between potentiallyinteracting π-systems, thereby minimizing π-π stacking.

Preferably, the moiety configured to reduce intermolecular interactionsis positioned at the periphery of the dye molecule, or at least at theperiphery of the substantially planar π-system. Typically,intermolecular π-interactions result from overlapping planes ofπ-systems. By positioning the moiety at the periphery of the dyemolecule, the moiety has a maximum effect in reducing the degree ofoverlap.

Generally, it is preferable to configure the dye molecule such that theaverage distance between the π-systems of adjacent molecules is greaterthan about 3.5 Å, more preferably greater than about 4 Å, and morepreferably greater than about 5 Å. This preferred distance between theπ-systems of adjacent molecules is based on theoretical calculations.From theoretical studies by the present inventors, it is understood thatπ-π interactions are significant at a distance of 3.5 Å or less.

Preferably, the moiety for reducing intermolecular interactions extendsout of the plane of the substantially planar π-system. Cyanine-typedyes, for example, typically comprise a π-system which forms a majorplane of the molecule. This major plane is usually comprised ofconjugated heteroaromatic and/or aromatic rings. Likewise, dithiolenedyes (e.g. nickel dithiolenes) typically have a substantially planarπ-system defined by a central nickel atom, two pairs of sulfur atoms anda pair of double bonds to which the sulfur atoms are vicinally bonded.The moiety is preferably configured, or can at least fold into aconformation, such that it extends out of this plane and exert stericrepulsion on neighbouring dye molecules. The greater the moiety extendsout of the plane of the π-system, the greater the reduction inintermolecular interactions will be.

Preferably, the moiety for reducing intermolecular interactions hasthree-dimensional structure. By “three-dimensional structure”, it ismeant that the moiety occupies a volume of three-dimensional space inall conformations. Preferably, the moiety is a three-dimensional C₃₋₃₀hydrocarbyl or C₃₋₃₀ hydrocarbylene group.

As will be apparent to the person skilled in the art, the exact natureof the three-dimensional hydrocarbyl or hydrocarbylene group is notcrucial to the present invention, provided that the group has sufficientthree-dimensional structure to inhibit intermolecular interactions.However, preferred moieties suitable for reducing intermolecularinteractions are C₃₋₃₀ bridged cyclic groups. As mentioned above, suchgroups are preferably positioned at the periphery of the π-system tomaximize their overlap-inhibiting effect.

As an alternative (or in addition to) the dye molecule comprising athree-dimensional hydrocarbyl or hydrocarbylene group, such as a bridgedcyclic group, it may comprise one or more polymeric substituents forreducing intermolecular interactions. In the context of the presentinvention, the term “polymeric” is used to describe a group having 2 ormore repeating monomer units. For example, the polymeric substituent forreducing intermolecular interactions may comprise from 2 to 5000repeating monomer units, more preferably 2 to 1000, more preferably 2 to100, and more preferably 2 to 50.

Without wishing to be bound by theory, it is understood by the presentinventors that polymeric substituents interfere with π-π interactions byfolding into conformations where at least part of the polymer ispositioned between π-systems of adjacent dye molecules. This inhibitsintermolecular π-π interactions and hence polymeric substituents canreduce the propensity for π-systems to overlap and interact.

It will be readily apparent that the exact nature of the polymericsubstituent(s) is not crucial provided that it is able to provide stericrepulsion. Accordingly, the substituent may comprise any type ofpolymer, such as polyethers, polyesters, polyamides, polyurethanes,polyalkenes etc.

The polymeric group may comprise a plurality of polymer chains in theform of a dendrimer—that is, a central core or template having aplurality of polymer chains radiating therefrom. The branched nature ofdendrimer molecules means that their polymeric chains are able to occupya large volume in three-dimensional space. This large three-dimensionalvolume is advantageous for increasing the steric repulsion betweenrespective dye molecules and, hence, reducing intermolecularinteractions.

In addition to providing steric repulsion, the polymeric substituent mayconfer additional properties on the dye molecule. For example, withappropriate selection of the polymeric substituent, it may be used toimpart hydrophilic properties on the molecule. Polymeric substituentscomprising repeating units of ethylene glycol (a PEG chain) areparticularly suitable for providing hydrophilicity, as well as reducingintermolecular π-interactions.

Preferably, the dye molecule comprises a hydrophilic group. Ahydrophilic group is preferred for imparting water-dispersibility orwater-solubility on the dye molecule. The dye molecules of the presentinvention are intended for use in inkjet ink compositions, preferablyaqueous inkjet ink compositions. Hence, the provision of a hydrophilicgroup is one means for allowing the dye molecules of the presentinvention to be dispersed in an aqueous inkjet ink composition.

Preferably, the hydrophilic group is selected from a hydrophilic polymerchain; an ammonium group; an acid group including salts thereof; or asulfonamide group.

An example of a hydrophilic polymeric chain is a PEG chain, which maycomprise from 2 to 5000 repeating units of ethylene glycol. Otherhydrophilic polymer chains will be readily apparent to the personskilled in the art. The hydrophilic polymer chain may be a substituent(or part of a substituent) on the dye molecule.

An ammonium group may be present as a substituent comprising a group ofgeneral formula —N⁺(R^(a))(R^(b))(R^(c)) or -U, wherein R^(a), R^(b),R^(c) may be the same or different and are independently selected fromH, C₁₋₈ alkyl (e.g. methyl, ethyl, cyclohexyl, cyclopentyl, tert-butyl,iso-propyl etc.), C₆₋₁₂ arylalkyl (e.g. benzyl, phenylethyl etc.) orC₆₋₁₂ aryl (e.g. phenyl, naphthyl etc.); and U is pyridinium,imidazolinium or pyrrolinium. Alternatively, the ammonium group may bepresent in the form of a quaternarized N atom in the dye molecule. Forexample, a heteroaromatic N atom in the dye molecule may bequaternarized with a C₁₋₈ alkyl or a C₆₋₁₂ arylalkyl group, inaccordance with known procedures.

An acid group may be present as a substituent comprising a group offormula —CO₂Z, —SO₃Z, —OSO₃Z, —PO₃Z₂ or —OPO₃Z₂, wherein Z is H or awater-soluble cation. Preferably, Z is selected from Li⁺, Na⁺ or K⁺.Methods of introducing acid groups, such as those described above, willbe well known to the person skilled in the art. For example, acarboxylic acid group may be introduced by oxidation of an olefinic orhydroxyl group in the dye molecule. Alternatively, a sulfonic acid group(—SO₃H) may be introduced to an aromatic moiety in the dye molecule bysulfonation using, for example, oleum or chlorosulfonic acid. Conversionof the acid group to its salt form can be effected using, for example, ametal hydroxide reagent (e.g. LiOH, NaOH or KOH) or a metal bicarbonate(e.g. NaHCO₃). Non-metal salts may also be prepared using, for example,an ammonium hydroxide (e.g. Bu₄NOH, NH₄OH etc.).

A sulfonamide group may be present as a substituent comprising a groupof general formula —SO₂NR^(p)R^(q), wherein R^(p) and R^(q) areindependently selected from H, C₁₋₈ alkyl (e.g. methyl, ethyl,cyclohexyl, cyclopentyl, tert-butyl, iso-propyl etc.),—(CH₂CH₂O)_(e)R^(e) (wherein e is an integer from 2 to 5000 and R^(e) isH, C₁₋₈ alkyl or C(O)C₁₋₈ alkyl), C₆₋₁₂ arylalkyl (e.g. benzyl,phenylethyl etc.) or C₆₋₁₂ aryl (e.g. phenyl, methoxyphenyl etc.).

The problem of absorption in the visible part of the spectrum is aparticular problem in IR-absorbing metal-ligand complexes. Metal-liganddye molecules are known in the art (e.g. nickel dithiolenes, metalphthalocyanines and metal naphthalocyanines). Hence, the presentinvention, in its preferred form, reduces intermolecular interactions inan IR-absorbing metal-ligand complex.

As used herein, the term “metal” includes any metal or semimetal (suchas Si or Ge) capable of forming a metal-ligand complex. Some examples ofsuch metals are Si, Ge, Ga, Mg, Al, Ti, V, Mn, Fe, Co, Ni, Cu, Zn, Sn,Pb, Zr, Pd and Pt. The metal may be in any suitable oxidation state forforming a metal-ligand complex. In the case of metal-cyanine dyes, themetal is preferably Si, Ge, Al, Mn, Ti, V, Zn or Sn. In the case ofmetal-dithiolene dyes, the metal is preferably Ni, Pd or Pt, morepreferably Ni.

The metal-ligand complex may have any ligand coordination structure,such as a tetra-coordinate (e.g. square planar), penta-coordinate (e.g.square pyramidal) or hexa-coordinate (e.g. octahedral) structure. Thestructure of the metal-ligand complex will depend on the nature of theligand and the metal, as well as the oxidation state of the metal.

Preferably, the metal-ligand complex comprises at least one multidentateligand. By “multidentate ligand”, it is meant a ligand having aplurality of coordinating atoms.

Multidentate ligands are preferred since their complexes with metals areusually more thermodynamically stable than their monodentatecounterparts. Moreover, multidentate ligands can form an extendedIR-absorbing π-system with the central metal atom of the metal-ligandcomplex via its coordinating heteroatoms and π-bond(s) in the ligandconjugated with the coordinating heteroatoms.

In a preferred method of the present invention, the metal-ligand dye ispreselected such that the ligand has at least one moiety, which extendsout of the plane of a substantially planar π-system. The structuralmoiety provides three-dimensional structure to an otherwisesubstantially planar dye molecule. Preferably, the metal-ligand dye ispreselected such that at least one ligand includes a bridged cyclicgroup.

In certain embodiments of the present invention, the dye molecule is ametal-ligand complex having an equatorial tetradentate cyanine-typeligand. Especially in such cases, vacant axial position(s) of thecomplex may be used to introduce further functional groups into themetal-ligand complex. Accordingly, in some forms of the presentinvention, the metal-ligand dye is preselected such that at least oneaxial ligand comprises a group for reducing intermolecular interactions.The axial ligand may comprise, for example, one or more polymericgroups. As already described above, polymeric groups can exist inconformations which reduce the propensity for π-systems of adjacent dyemolecules to interact. Hence, polymeric axial ligands can further assistin reducing intermolecular interactions.

Preferably, the axial ligand adopts a conformation (or is configured)such that it effectively “protects” or blocks a π-face of the dyemolecule. An axial ligand, which can form an “umbrella” over theπ-system and reduce intermolecular interactions between adjacent dyemolecules is particularly suitable for use in the present invention.

In order for the axial ligand to have maximum steric repulsion, it maycomprise a plurality of chains, such as polymer chains, in the form of adendrimer—that is, a central core or template having a plurality ofchains radiating therefrom. Dendrimers will be well known to the skilledperson and are described in more detail below.

Notwithstanding the advantageous use of axial ligand(s) to reduceintermolecular interactions, the axial ligand(s) may also provide thedye molecule with hydrophilicity. For example, if the axial ligand(s)comprise one or more hydrophilic groups, they will provide the dyemolecule with water-dispersibility. As mentioned above, waterdispersibilty is advantageous, since the dye molecules may be used inaqueous inkjet ink compositions. Examples of hydrophilic groups are PEGchains, ammonium groups and acid groups (including salts thereof).Accordingly, an axial ligand comprising a dendrimer with hydrophilicgroup(s) will impart the dual properties of (1) reducing intermolecularinteractions, and (2) increasing water-dispersibility of the dyemolecule.

In some embodiments of the present invention, the dye is a cyanine-typedye, which is preselected from a complex of formula (I) or a compound offormula (II):

where

-   Q¹, Q², Q³ and Q⁴ are the same or different and are independently    selected from a C₃₋₂₀ arylene group or a C₃₋₂₀ heteroarylene group,    said C₃₋₂₀ arylene or-   C₃₋₂₀ heteroarylene group including at least one substituent    suitable for reducing intermolecular interactions;-   M is selected from Si(A¹)(A²), Ge(A¹)(A²), Ga(A¹), Mg, Al(A¹), TiO,    Ti(A¹)(A²), ZrO, Zr(A¹)(A²), VO, V(A¹)(A²), Mn, Mn(A¹), Fe, Fe(A¹),    Co, Ni, Cu, Zn, Sn, Sn(A¹)(A²), Pb, Pb(A¹)(A²), Pd and Pt;-   A¹ and A² are axial ligands, which may be the same or different, and    are selected from —OH, halogen, —OR³, a hydrophilic ligand and/or a    ligand suitable for reducing intermolecular interactions;-   R³ is a selected from C₁₋₁₂ alkyl, C₅₋₁₂ aryl, C₅₋₁₂ arylalkyl or    Si(R^(x))(R^(y))(R^(z)); and-   R^(x), R^(y) and R^(z) may be the same or different and are selected    from C₁₋₁₂ alkyl, C₅₋₁₂ aryl, C₅₋₁₂ arylalkyl, C₁₋₁₂ alkoxy, C₅₋₁₂    aryloxy or C₅₋₁₂ arylalkoxy.

Q¹, Q², Q³ and Q⁴ may be the same or different from each other.Generally, cyanine-type dyes are symmetrical structures synthesized by acascaded coupling of vicinal cyano groups to form a macrocyclic ring.For example, the dye of formula (I) above may be prepared by a cascadedbase-catalysed coupling of four dicyano compounds of general formula (1)or four imidine compounds of formula (2):

The cascaded base-catalysed reaction may be facilitated by metaltemplating, or it may proceed in the absence of a metal. Accordingly, bythe nature of this preferred synthesis of cyanine-type compounds, thegroups represented as Q¹, Q², Q³ and Q⁴ will usually be the same or atleast have the same core structural units. However, in cases where thecompound is functionalized after macrocycle formation, the groupsrepresented by Q¹, Q², Q³ and Q⁴ may be different. For example,functionalization of aromatic moieties subsequent to macrocycleformation may not occur entirely symmetrically, in which case Q¹, Q², Q³and Q⁴ may be different from each other by virtue of different numbersof substituents.

Preferably, the groups represented as Q¹, Q², Q³ and Q⁴ are selectedfrom an arylene or heteroarylene group of formula (i) to (vii) below:

wherein:

-   R¹ and R² may be the same or different and are selected from    hydrogen, hydroxyl, C₁₋₁₂ alkyl, C₁₋₁₂ alkyl bearing a hydrophilic    or hydrophilizable group, C₁₋₁₂ alkoxy, C₁₋₁₂ alkoxy bearing a    hydrophilic or hydrophilizable group, amino, C₁₋₁₂ alkylamino,    di(C₁₋₁₂ alkyl)amino, halogen, cyano, thiol, C₁₋₁₂ alkylthio, nitro,    carboxy, C₁₋₁₂ alkylcarbonyl, C₁₋₁₂ alkoxycarbonyl, C₁₋₁₂    alkylcarbonyloxy or C₁₋₁₂ alkylcarbonylamino;-   T is selected from a substituent comprising a polymeric chain or a    C₃₋₃₀ hydrocarbyl group having three-dimensional structure;-   W is a hydrophilic group;-   E is selected from —OH, —O⁻, C₁₋₆ alkyl, carboxy-C₁₋₆ alkyl,    sulfo-C₁₋₆ alkyl, C₁₋₆ alkoxy, C₅₋₁₂ arylalkyl, C₁₋₆ alkylcarbonyl,    C₅₋₁₂ arylalkylcarbonyl, C₁₋₆ alkoxycarbonyl or C₅₋₁₂    arylalkoxycarbonyl;-   m is 0, 1 or 2;-   n is 1 or 2; and-   p is 0, 1 or 2.

Preferably, Q¹, Q², Q³ and Q⁴ are of formula (v).

The groups represented by R¹ and R² are primarily for modifying or“tuning” the wavelength of λ_(max) of the dye. Electron-donatingsubstituents (e.g. alkoxy, alkylamino) at these positions can produce ared-shift in the dye. Conversely electron-withdrawing substituents atthese positions (e.g. cyano, carboxy, nitro) can produce a blue-shift inthe dye. By varying these substituents, the dye may be “tuned” to thefrequency of a particular laser detector.

In a preferred embodiment of the present invention, R¹ and R² are bothC₁₋₈ alkoxy groups, preferably butoxy. Butoxy substituentsadvantageously shift the λ_(max) towards longer wavelengths in the nearinfrared, which are preferable for detection by commercially availablelasers.

In an alternative preferred embodiment R¹ and R² are C₁₋₁₂ alkoxy groupsbearing a hydrophilic or hydrophilizable group. C₁₋₁₂ alkoxy groupsbearing a hydrophilic or hydrophilizable group are advantageous sincethey provide the dual functions of (i) tuning the absorption frequencyof the dye, and (ii) providing hydrophilicity to aidwater-dispersibility. The hydrophilic group may be a hydrophilic polymerchain; an ammonium group; an acid group including salts thereof; or asulfonamide group, as defined above. The hydrophilizable group may be ahydroxyl, protected hydroxyl, amino, protected amino, thiol, protectedthiol, cyano, ester, halogen or alkenyl group. Such groups may bereadily converted into hydrophilic groups. For example, hydroxyl groupsmay be oxidized to carboxylic acid groups (including salts thereof);hydroxyl groups may be coupled to PEG chains; amino groups may bequaternarized using, for example, methyl iodide; thiol groups may beoxidized to sulfonic acid groups (including salts thereof) orsulfonamides; cyano and ester groups may be hydrolysed to carboxylicacid groups (including salts thereof); and alkenyl groups may beoxidatively cleaved (e.g. by ozonolysis or permanganate oxidation) toprovide carboxylic acid groups (including salts thereof). In the case ofprotected heteroatoms, the protecting group is removed before conversionto a hydrophilic group. Hence, R¹ and R² both may be a hydroxyalkoxygroup such as —O(CH₂)₄OH.

The group(s) represented by T reduces intermolecular interactionsbetween dye molecules. The suffix n in T_(m) and the suffix p in T_(p)indicate the number of T substituents. In cases where there are two Tsubstituents, these may be joined to form a cyclic structure.Preferably, T is a substituent comprising a C₃₋₃₀ bridged carbocycle,such as those described above. Alternatively, T is a substituentcomprising a polymeric chain, such as those described above. In allcases, the dye comprises at least one moiety suitable for reducingintermolecular interactions.

The group(s) represented by W, when present, imparts hydrophilicity tothe dye molecule. The suffix m in T_(m) indicates the number of Wsubstituents. Each of Q¹, Q², Q³ and Q⁴ may have different numbers of Wsubstituents arising, for example, from unsymmetrical sulfonations.Preferably, W is selected from a substituent comprising a PEG chain; asubstituent comprising an ammonium group; a substituent comprising anacid group, including salts thereof; or a substituent comprising asulfonamide group. W may be any one of the preferred hydrophilic groupsdescribed above. Preferably, W is —SO₃H or a water-soluble salt thereof,such as Li, Na⁺, K⁺, NH₄ ⁺ etc. Sulfonic acid groups may be easilyintroduced into any of aromatic structures (i) to (v) by sulfonationusing, for example, oleum or chlorosulfonic acid. Alternatively (or inaddition), hydrophilicity may be imparted into the dye molecule byquaternarizing an N atom. This is shown in heteroaromatic moieties (vi)and (vii).

Preferably, the dye molecule contains a central metal atom andcorresponds to a compound of formula (I). Metal-ligand dye molecules offormula (I) are preferred, since metal atoms (or ions) can be used totune the absorption λ_(max) of the molecule to a preferred wavelength.For example, certain metals such as Mn, V and Sn can produce largered-shifts in the λ_(max). In this context, red-shift means a shift ofλ_(max) towards longer wavelengths as compared to the metal-freecompound.

The degree of red-shift may be influenced by the oxidation state of themetal. High oxidation states (e.g. V(IV), Mn(III) and Sn(IV)) will tendto produce large red-shifts, while low oxidation states (e.g. Mn (II)and Sn(II)) will tend to produce smaller red-shifts.

Metal atoms having one or more axial ligands may be used in the presentinvention. As described above, axial ligands may be used as a handle forintroducing additional or supplemental functionalities into the dyemolecule. Accordingly, M is preferably Ti(A¹)(A²), Zr(A¹)(A²),V(A¹)(A²), Si(A¹)(A²), Ge(A¹)(A²), Ga(A¹), Al(A¹), Mn(A¹), Fe(A¹),Sn(A¹)(A²), or Pb(A¹)(A²). Si(A¹)(A²) is particularly preferred due itslow cost and low toxicity. Mn(A¹) is also preferred since it offers theadvantages of a large red-shift in addition to its potential forfunctionalizing the dye molecule via its axial ligand. In cases wherethere are two axial ligands, these may be on opposite faces or they maybe intermolecular. The geometry of the ligands is generally dictated bythe metal and its preferred bonding geometry.

A¹ and A² may be selected to add axial steric bulk to the dye molecule,thereby reducing intermolecular interactions even further.

Alternatively (or in addition), A¹ and/or A² may be selected to addhydrophilicity to the dye molecule. Hence, A¹ and/or A² may include ahydrophilic group, such as any one of the groups defined as W above.

In order to introduce axial steric bulk and/or increase hydrophilicity,A¹ and/or A² are preferably dendrimers. In one preferred form A¹ and/orA² is a ligand of formula (IIIa):

wherein:

-   C¹ represents a core unit having two or more branching positions;-   each P¹ is independently selected from H, a hydrophilic moiety or a    branched moiety;-   g¹ is an integer from 2 to 8;-   q¹ is 0 or an integer from 1 to 6;-   each p¹ is independently selected from 0 or an integer from 1 to 6;

Preferably, the core unit C¹ is selected from a C atom, an N atom, a Siatom, a C₁₋₈ alkyl residue, a C₃₋₈ cycloalkyl residue, or a phenylresidue. The core unit C¹ has at least two branching positions, thenumber of branching positions corresponding to the value of g¹. Hence,an axial ligand having 3 branching positions and a carbon atom core(i.e. g¹=3; C¹=C atom) may be, for example, a pentaerythritol derivativeof formula (A):

Each P¹ group in formula (IIIa) may be the same or different. Forexample, in a pentaerythritol derivative (having three branchingpositions), there may be two arms bearing terminal hydroxyl groups(—CH₂OH; P¹=H) and one arm bearing a sulfate group (—CH₂OSO₃Z; P¹=SO₃Z).

Preferably, P¹ is a hydrophilic moiety. The hydrophilic moiety may be anacid group (including salts thereof), a sulfonamide group, a hydrophilicpolymer chain or an ammonium group.

Accordingly, P¹ may comprise a hydrophilic polymer chain, such as a PEGchain. Hence, in some embodiments, P¹ may be of formula:(CH₂CH₂O)_(v)R⁶, wherein v is an integer from 2 to 5000 (preferably 2 to1000, preferably 2 to 100) and R⁶ is H, C₁₋₆ alkyl or C(O)C₁₋₈ alkyl.

Alternatively, P¹ may comprise an acid group (including salts thereof),such as sulfonic acids, sulfates, phosphonic acids, phosphates,carboxylic acids, carboxylates etc. Hence, in some embodiments P¹ may beof formula: SO₃Z, PO₃Z₂, C₁₋₁₂ alkyl-CO₂Z, C₁₋₁₂ alkyl-SO₃Z orC₁₋₁₂-alkyl-PO₃Z₂, C₁₋₁₂ alkyl-OSO₃Z or C₁₋₁₂-alkyl-OPO₃Z₂ wherein Z isH or a water-soluble cation. Examples of water-soluble cations are Li⁺,Na⁺, K⁺, NH₄ ⁺ etc.

Alternatively, P¹ may comprise an ammonium group, such as a quaternaryammonium group. Hence, in some embodiments P¹ may be of formula:C₁₋₁₂-alkyl-N⁺(R^(a))(R^(b))(R^(c)) or C₁₋₁₂ alkyl-U, wherein R^(a),R^(b), R^(c) may be the same or different and are independently selectedfrom H, C₁₋₈ alkyl (e.g. methyl, ethyl, cyclohexyl, cyclopentyl,tert-butyl, iso-propyl etc.) or C₆₋₁₂ arylalkyl (e.g. benzyl,phenylethyl etc. or C₆₋₁₂ aryl (e.g. phenyl, naphthyl etc.) and U ispyridinium, imidazolinium or pyrrolinium.

Alternatively, P¹ may comprise a sulfonamide group, such as a group ofgeneral formula —SO₂NR^(p)R^(q), wherein R^(p) and R^(q) areindependently selected from H, C₁₋₈ alkyl (e.g. methyl, ethyl,cyclohexyl, cyclopentyl, tert-butyl, iso-propyl etc.),—(CH₂CH₂O)_(e)R^(e) (wherein e is an integer from 2 to 5000 and R^(e) isH, C₁₋₈ alkyl or C(O)C₁₋₈ alkyl), C₆₋₁₂ arylalkyl (e.g. benzyl,phenylethyl etc.) or C₆₋₁₂ aryl (e.g. phenyl, methoxyphenyl etc.).

Branched structures such as those described above are generally known asdendrimers. Dendrimers are advantageous since their branched chainsmaximize the effective three-dimensional volume of the axial ligand and,in addition, provide the potential for introducing a plurality ofhydrophilic groups into the dye molecule. The pentaerythritol structureshown in formula (A) is an example of a simple dendrimer suitable foruse in the present invention. Further examples are triethanolaminederivatives (B), phloroglucinol derivatives (C), and 3,5-dihydroxybenzylalcohol derivatives (D):

In an alternative embodiment, one or more of the P¹ groups is itself abranched moiety. The branched moiety may be any structure adding furtherbranching to the axial ligand, such as a moiety of formula (IIIb):

wherein:

-   C² represents a core unit having two or more branching positions;-   P² is H or a hydrophilic moiety;-   g² is an integer from 2 to 8;-   q² is 0 or an integer from 1 to 6;-   p² is 0 or an integer from 1 to 6;

Preferred forms of C₂ and P² correspond to the preferred forms of C¹ andP¹ described above. A specific example of an axial ligand, wherein P¹ isa branched moiety of formala (IIIb) is dipentaerythritol derivative (E):

Alternatively, the branched moiety may comprise multiple randomizedbranched chains, based on motifs of core units linked by alkylene orether chains. It will be readily understood that randomized dendrimerstructures may be rapidly built up by, for example, successiveetherifications of pentaerythritol with further pentaerythritol,3,5-dihydroxybenzyl alcohol or triethanolamine moieties. One or moreterminal hydroxyl groups on the dendrimer may be capped with hydrophilicgroups, such as any of the hydrophilic groups above described. Theextent of hydrophilic capping may be used to control thewater-solubility of the dye molecule.

It will be appreciated that randomized branched structures cannot bereadily illustrated using precise structural formulae. However, allbranched dendrimer-like structures are contemplated within the scope ofthe above definitions of A¹ and A².

In other embodiments of the present invention, the metal-ligand dye ispreselected from a metal dithiolene of formula (X):

-   M² is selected from Ni, Pd or Pt (preferably Ni);-   j is selected from 1, 2, 3 or 4;-   k is selected from 1, 2, 3 or 4;-   n is selected from 0, 1 or 2;-   W is a hydrophilic group, as defined above;-   up to three —(CH₂)— groups in the carbocycle may be optionally    replaced by a group independently selected from —C(O)—, —NH—, —S—,    —O—;-   up to three —CH— groups in the carbocycle may be optionally replaced    by —N—; and-   up to four H atoms in the carbocycle may be optionally replaced a    group independently selected from C₁₋₆ alkyl, C₁₋₆ alkoxy, C₅₋₁₂    aryl, C₅₋₁₂ arylalkyl, halogen, hydroxyl or amino.

This preferred dye is characterized in that the dithiolene ligands arebridged carbocycles.

In one preferred form, j is 1 and k is 2. Further, the dye moleculepreferably comprises —C(Me)₂— bridging groups. In other words, theligands are preferably bornene derivatives. Bornene derivatives areadvantageous, since they are readily available commercially atrelatively low cost.

The group(s) represented by W imparts hydrophilicity to the dyemolecule. Preferably, W is of formula —(CH₂)_(t)—SO₃Z, wherein t is 0 oran integer from 1 to 6, and Z is H or a water-soluble cation. Morepreferably, in this embodiment of the invention, W is of formula—CH₂SO₃H, —CH₂SO₃Na or —CH₂SO₃K.

A particularly preferred dye molecule according to the present inventionis shown in formula (III) below:

This compound has excellent water-dispersibility combined with minimalabsorption in the visible region of the spectrum. It absorbs strongly inthe near infrared region at a λ_(max) of 781 nm.

The term “hydrocarbyl” is used herein to refer to monovalent groupsconsisting generally of carbon and hydrogen. Hydrocarbyl groups thusinclude alkyl, alkenyl and alkynyl groups (in both straight and branchedchain forms), carbocyclic groups (including polycycloalkyl groups suchas bicyclooctyl and adamantyl) and aryl groups, and combinations of theforegoing, such as alkylcycloalkyl, alkylpolycycloalkyl, alkylaryl,alkenylaryl, alkynylaryl, cycloalkylaryl and cycloalkenylaryl groups.Similarly, the term “hydrocarbylene” refers to divalent groupscorresponding to the monovalent hydrocarbyl groups described above.

Unless specifically stated otherwise, up to four —C—C— and/or —C—Hmoieties in the hydrocarbyl group may be optionally interrupted by oneor more moieties selected from —O—; —NR^(w)—; —S—; —C(O)—; —C(O)O—;—C(O)NR^(w)—; —S(O)—; —SO₂—; —SO₂O—; —SO₂NR^(w)—; where R^(w) is a groupselected from H, C₁₋₁₂ alkyl, C₆₋₁₂ aryl or C₆₋₁₂ arylalkyl.

Unless specifically stated otherwise, where the hydrocarbyl groupcontains one or more —C═C— moieties, up to four —C═C— moieties mayoptionally be replaced by —C═N—. Hence, the term “hydrocarbyl” mayinclude moieties such as heteroaryl, ether, thioether, carboxy,hydroxyl, alkoxy, amine, thiol, amide, ester, ketone, sulfoxide,sulfonate, sulfonamide etc.

Unless specifically stated otherwise, the hydrocarbyl group may compriseup to four substituents independently selected from halogen, cyano,nitro, a hydrophilic group as defined above (e.g. —SO₃H, —SO₃K, —CO₂Na,—NH₃ ⁺, —NMe₃ ⁺ etc.) or a polymeric group as defined above (e.g. apolymeric group derived from polyethylene glycol).

As used herein, the term “bridged cyclic group” includes C₄₋₃₀carbocycles (preferably C₆₋₂₀ carbocycles) containing 1, 2, 3 or 4bridging atoms. Examples of bridged carbocyclic groups are bornyl andtriptycenyl, and derivatives thereof. The term “bridged cyclic group”also includes bridged polycyclic groups, including groups such asadamantanyl and tricyclo[5.2.1.0]decanyl, and derivatives thereof.

Unless specifically stated otherwise, the term “bridged cyclic group”also includes bridged carbocycles wherein 1, 2, 3 or 4 carbon atoms arereplaced by heteroatoms selected from N, S or O (i.e. bridgedheterocycles). When it is stated that a carbon atom in a carbocycle isreplaced by a heteroatom, what is meant is that —CH— is replaced by —N—,—CH₂— is replaced by —O—, or —CH₂— is replaced by —S—. Hence, the term“bridged cyclic group” includes bridged heterocyclic groups, such asquinuclidinyl and tropanyl. Unless specifically stated otherwise, any ofthe bridged cyclic groups may be optionally substituted with 1, 2, 3 or4 of the substituents described below.

The term “aryl” is used herein to refer to an aromatic group, such asphenyl, naphthyl or triptycenyl. C₆₋₁₂ aryl, for example, refers to anaromatic group having from 6 to 12 carbon atoms, excluding anysubstituents. The term “arylene”, of course, refers to divalent groupscorresponding to the monovalent aryl groups described above. Anyreference to aryl implicitly includes arylene, where appropriate.

The term “heteroaryl” refers to an aryl group, where 1, 2, 3 or 4 carbonatoms are replaced by a heteroatom selected from N, O or S. Examples ofheteroaryl (or heteroaromatic) groups include pyridyl, benzimidazolyl,indazolyl, quinolinyl, isoquinolinyl, indolinyl, isoindolinyl, indolyl,isoindolyl, furanyl, thiophenyl, pyrrolyl, thiazolyl, imidazolyl,oxazolyl, isoxazolyl, pyrazolyl, isoxazolonyl, piperazinyl, pyrimidinyl,piperidinyl, morpholinyl, pyrrolidinyl, isothiazolyl, triazolyl,oxadiazolyl, thiadiazolyl, pyridyl, pyrimidinyl, benzopyrimidinyl,benzotriazole, quinoxalinyl, pyridazyl, coumarinyl etc. The term“heteroarylene”, of course, refers to divalent groups corresponding tothe monovalent heteroaryl groups described above. Any reference toheteroaryl implicitly includes heteroarylene, where appropriate.

Unless specifically stated otherwise, aryl, arylene, heteroaryl andheteroarylene groups may be optionally substituted with 1, 2, 3, 4 or 5of the substituents described below.

Where reference is made to optionally substituted groups (e.g. inconnection with bridged cyclic groups, aryl groups or heteroarylgroups), the optional substituent(s) are independently selected fromC₁₋₈ alkyl, C₁₋₈ alkoxy, —(OCH₂CH₂)_(d)OR^(d) (wherein d is an integerfrom 2 to 5000 and R^(d) is H, C₁₋₈ alkyl or C(O)C₁₋₈ alkyl), cyano,halogen, amino, hydroxyl, thiol, —SR^(v), —NR^(u)R^(v), nitro, phenyl,phenoxy, —CO₂R^(v), —C(O)R^(v), —OCOR^(v), —SO₂R^(v), —OSO₂R^(v),—SO₂₀R^(v), —NHC(O)R^(v), —CONR^(u)R^(v), —CONR^(u)R^(v),—SO₂NR^(u)R^(v), wherein R^(u) and R^(v) are independently selected fromhydrogen, C₁₋₁₂ alkyl, phenyl or phenyl-C₁₋₈ alkyl (e.g. benzyl). Where,for example, a group contains more than one substituent, differentsubstituents can have different R^(u) or R^(v) groups. For example, anaphthyl group may be substituted with three substituents: —SO₂NHPh,—CO₂Me group and —NH₂.

The term “alkyl” is used herein to refer to alkyl groups in bothstraight and branched forms, The alkyl group may be interrupted with 1,2 or 3 heteroatoms selected from O, N or S. The alkyl group may also beinterrupted with 1, 2 or 3 double and/or triple bonds. However, the term“alkyl” usually refers to alkyl groups having no heteroatominterruptions or double or triple bond interruptions. Where “alkenyl”groups are specifically mentioned, this is not intended to be construedas a limitation on the definition of “alkyl” above.

Where reference is made to, for example, C₁₋₁₂ alkyl, it is meant thealkyl group may contain any number of carbon atoms between 1 and 12.Unless specifically stated otherwise, any reference to “alkyl” meansC₁₋₁₂ alkyl, preferably C₁₋₆ alkyl.

The term “alkyl” also includes cycloalkyl groups. As used herein, theterm “cycloalkyl” includes cycloalkyl, polycycloalkyl, and cycloalkenylgroups, as well as combinations of these with linear alkyl groups, suchas cycloalkylalkyl groups. The cycloalkyl group may be interrupted with1, 2 or 3 heteroatoms selected from O, N or S. However, the term“cycloalkyl” usually refers to cycloalkyl groups having no heteroatominterruptions. Examples of cycloalkyl groups include cyclopentyl,cyclohexyl, cyclohexenyl, cyclohexylmethyl and adamantyl groups.

The term “arylalkyl” refers to groups such as benzyl, phenylethyl andnaphthylmethyl.

The term “halogen” or “halo” is used herein to refer to any of fluorine,chlorine, bromine and iodine. Usually, however, refers to chlorine orfluorine substituents.

Where reference is made to “a substituent comprising . . . ” (e.g. “asubstituent comprising a hydrophilic group”, “a substituent comprisingan acid group (including salts thereof)”, “a substituent comprising apolymeric chain” etc.), the substituent in question may consist entirelyor partially of the group specified. For example, “a substituentcomprising an acid group (including salts thereof)” may be of formula—(CH₂)_(j)—SO₃K, wherein j is 0 or an integer from 1 to 6. Hence, inthis context, the term “substituent” may be, for example, an alkylgroup, which has a specified group attached. However, it will be readilyappreciated that the exact nature of the substituent is not crucial tothe desired functionality, provided that the specified group is present.

Chiral compounds described herein have not been givenstereo-descriptors. However, when compounds may exist in stereoisomericforms, then all possible stereoisomers and mixtures thereof are included(e.g. enantiomers, diastereomers and all combinations including racemicmixtures etc.).

Likewise, when compounds may exist in a number of regioisomeric forms,then all possible regioisomers and mixtures thereof are included.

For the avoidance of doubt, the term “a” (or “an”), in phrases such as“comprising a”, means “at least one” and not “one and only one”. Wherethe term “at least one” is specifically used, this should not beconstrued as having a limitation on the definition of “a”.

Throughout the specification, the term “comprising”, or variations suchas “comprise” or “comprises”, should be construed as including a statedelement, integer or step, but not excluding any other element, integeror step.

Inkjet Inks

The method of the present invention is particularly suitable for usewith inkjet ink compositions, preferably water-based inkjet inks. Hence,the present invention provides method of minimizing absorption ofvisible light in an inkjet ink comprising an IR-absorbing dye, saidmethod comprising reducing intermolecular interactions between adjacentdye molecules.

Water-based inkjet ink compositions are well known in the literatureand, in addition to water, may comprise additives, such as co-solvents,biocides, sequestering agents, humectants, pH adjusters, viscositymodifiers, penetrants, wetting agents, surfactants etc.

Co-solvents are typically water-soluble organic solvents. Suitablewater-soluble organic solvents include C₁₋₄ alkyl alcohols, such asethanol, methanol, butanol, propanol, and 2-propanol; glycol ethers,such as ethylene glycol monomethyl ether, ethylene glycol monoethylether, ethylene glycol monobutyl ether, ethylene glycol monomethyl etheracetate, diethylene glycol monomethyl ether, diethylene glycol monoethylether, diethylene glycol mono-n-propyl ether, ethylene glycolmono-isopropyl ether, diethylene glycol mono-isopropyl ether, ethyleneglycol mono-n-butyl ether, diethylene glycol mono-n-butyl ether,triethylene glycol mono-n-butyl ether, ethylene glycol mono-t-butylether, diethylene glycol mono-t-butyl ether, 1-methyl-1-methoxybutanol,propylene glycol monomethyl ether, propylene glycol monoethyl ether,propylene glycol mono-t-butyl ether, propylene glycol mono-n-propylether, propylene glycol mono-isopropyl ether, dipropylene glycolmonomethyl ether, dipropylene glycol monoethyl ether, dipropylene glycolmono-n-propyl ether, dipropylene glycol mono-isopropyl ether, propyleneglycol mono-n-butyl ether, and dipropylene glycol mono-n-butyl ether;formamide, acetamide, dimethyl sulfoxide, sorbitol, sorbitan, glycerolmonoacetate, glycerol diacetate, glycerol triacetate, and sulfolane; orcombinations thereof.

Other useful water-soluble organic solvents include polar solvents, suchas 2-pyrrolidone, N-methylpyrrolidone, ε-caprolactam, dimethylsulfoxide, sulfolane, morpholine, N-ethylmorpholine,1,3-dimethyl-2-imidazolidinone and combinations thereof.

The inkjet ink may contain a high-boiling water-soluble organic solventwhich can serve as a wetting agent or humectant for imparting waterretentivity and wetting properties to the ink composition. Such ahigh-boiling water-soluble organic solvent includes one having a boilingpoint of 180° C. or higher. Examples of the water-soluble organicsolvent having a boiling point of 180° C. or higher are ethylene glycol,propylene glycol, diethylene glycol, pentamethylene glycol, trimethyleneglycol, 2-butene-1,4-diol, 2-ethyl-1,3-hexanediol,2-methyl-2,4-pentanediol, tripropylene glycol monomethyl ether,dipropylene glycol monoethyl glycol, dipropylene glycol monoethyl ether,dipropylene glycol monomethyl ether, dipropylene glycol, triethyleneglycol monomethyl ether, tetraethylene glycol, triethylene glycol,diethylene glycol monobutyl ether, diethylene glycol monoethyl ether,diethylene glycol monomethyl ether, tripropylene glycol, polyethyleneglycols having molecular weights of 2000 or lower, 1,3-propylene glycol,isopropylene glycol, isobutylene glycol, 1,4-butanediol, 1,3-butanediol,1,5-pentanediol, 1,6-hexanediol, glycerol, erythritol, pentaerythritoland combinations thereof.

The total water-soluble organic solvent content in the inkjet ink ispreferably about 5 to 50% by weight, more preferably 10 to 30% byweight, based on the total ink composition.

Other suitable wetting agents or humectants include saccharides(including monosaccharides, oligosaccharides and polysaccharides) andderivatives thereof (e.g. maltitol, sorbitol, xylitol, hyaluronic salts,aldonic acids, uronic acids etc.)

The inkjet ink may also contains a penetrant for acceleratingpenetration of the aqueous ink into the recording medium. Suitablepenetrants include polyhydric alcohol alkyl ethers (glycol ethers)and/or 1,2-alkyldiols. Examples of suitable polyhydric alcohol alkylethers are ethylene glycol monomethyl ether, ethylene glycol monoethylether, ethylene glycol monobutyl ether, ethylene glycol monomethyl etheracetate, diethylene glycol monomethyl ether, diethylene glycol monoethylether, ethylene glycol mono-n-propyl ether, ethylene glycolmono-isopropyl ether, diethylene glycol mono-isopropyl ether, ethyleneglycol mono-n-butyl ether, diethylene glycol mono-n-butyl ether,triethylene glycol mono-n-butyl ether, ethylene glycol mono-t-butylether, diethylene glycol mono-t-butyl ether, 1-methyl-1-methoxybutanol,propylene glycol monomethyl ether, propylene glycol monoethyl ether,propylene glycol mono-t-butyl ether, propylene glycol mono-n-propylether, propylene glycol mono-isopropyl ether, dipropylene glycolmonomethyl ether, dipropylene glycol monoethyl ether, dipropylene glycolmono-n-propyl ether, dipropylene glycol mono-isopropyl ether, propyleneglycol mono-n-butyl ether, and dipropylene glycol mono-n-butyl ether.Examples of suitable 1,2-alkyldiols are 1,2-pentanediol and1,2-hexanediol. The penetrant may also be selected from straight-chainhydrocarbon diols, such as 1,3-propanediol, 1,4-butanediol,1,5-pentanediol, 1,6-hexanediol, 1,7-heptanediol, and 1,8-octanediol.Glycerol may also be used as a penetrant.

The amount of penetrant is preferably in the range of 1 to 20% byweight, more preferably 1 to 10% by weight, based on the total inkcomposition.

The inkjet ink may also contain a surface active agent, especially ananionic surface active agent and/or a nonionic surface active agent.Useful anionic surface active agents include sulfonic acid types, suchas alkanesulfonic acid salts, α-olefinsulfonic acid salts,alkylbenzenesulfonic acid salts, alkylnaphthalenesulfonic acids,acylmethyltaurines, and dialkylsulfosuccinic acids; alkylsulfuric estersalts, sulfated oils, sulfated olefins, polyoxyethylene alkyl ethersulfuric ester salts; carboxylic acid types, e.g., fatty acid salts andalkylsarcosine salts; and phosphoric acid ester types, such asalkylphosphoric ester salts, polyoxyethylene alkyl ether phosphoricester salts, and glycerophosphoric ester salts. Specific examples of theanionic surface active agents are sodium dodecylbenzenesulfonate, sodiumlaurate, and a polyoxyethylene alkyl ether sulfate ammonium salt.

Suitable nonionic surface active agents include ethylene oxide adducttypes, such as polyoxyethylene alkyl ethers, polyoxyethylene alkylphenylethers, polyoxyethylene alkyl esters, and polyoxyethylene alkylamides;polyol ester types, such as glycerol alkyl esters, sorbitan alkylesters, and sugar alkyl esters; polyether types, such as polyhydricalcohol alkyl ethers; and alkanolamide types, such as alkanolamine fattyacid amides. Specific examples of nonionic surface active agents areethers such as polyoxyethylene nonylphenyl ether, polyoxyethyleneoctylphenyl ether, polyoxyethylene dodecylphenyl ether, polyoxyethylenealkylallyl ether, polyoxyethylene oleyl ether, polyoxyethylene laurylether, and polyoxyalkylene alkyl ethers (e.g. polyoxyethylene alkylethers); and esters, such as polyoxyethylene oleate, polyoxyethyleneoleate ester, polyoxyethylene distearate, sorbitan laurate, sorbitanmonostearate, sorbitan mono-oleate, sorbitan sesquioleate,polyoxyethylene mono-oleate, and polyoxyethylene stearate. Acetyleneglycol surface active agents, such as2,4,7,9-tetramethyl-5-decyne-4,7-diol, 3,6-dimethyl-4-octyne-3,6-diol or3,5-dimethyl-1-hexyn-3-ol, may also be used.

The inkjet ink may contain a pH adjuster for adjusting its pH to 7 to 9.Suitable pH adjusters include basic compounds, such as sodium hydroxide,potassium hydroxide, lithium hydroxide, sodium carbonate, sodiumhydrogencarbonate, potassium carbonate, potassium hydrogencarbonate,lithium carbonate, sodium phosphate, potassium phosphate, lithiumphosphate, potassium dihydrogenphosphate, dipotassium hydrogenphosphate,sodium oxalate, potassium oxalate, lithium oxalate, sodium borate,sodium tetraborate, potassium hydrogenphthalate, and potassiumhydrogentartrate; ammonia; and amines, such as methylamine, ethylamine,diethylamine, trimethylamine, triethylamine,tris(hydroxymethyl)aminomethane hydrochloride, triethanolamine,diethanolamine, diethylethanolamine, triisopropanolamine,butyldiethanolamine, morpholine, and propanolamine.

The inkjet ink may also include a biocide, such as benzoic acid,dichlorophene, hexachlorophene, sorbic acid, hydroxybenzoic esters,sodium dehydroacetate, 1,2-benthiazolin-3-one, 3,4-isothiazolin-3-one or4,4-dimethyloxazolidine.

The inkjet ink may also contain a sequestering agent, such asethylenediaminetetraacetic acid (EDTA).

The inkjet ink may also contain a singlet oxygen quencher. The presenceof singlet oxygen quencher(s) in the ink reduces the propensity for theIR-absorbing dye to degrade. The quencher consumes any singlet oxygengenerated in the vicinity of the dye molecules and, hence, minimizestheir degradation. An excess of singlet oxygen quencher is advantageousfor minimizing degradation of the dye and retaining its IR-absorbingproperties over time. Preferably, the singlet oxygen quencher isselected from ascorbic acid, 1,4-diazabicyclo-[2.2.2]octane (DABCO),azides (e.g. sodium azide), histidine or tryptophan.

Inkjet Printers

The inkjet ink in the method described above may be contained in an inkreservoir in fluid communication with a printhead of an inkjet printer.

Inkjet printers, such as thermal bubble-jet and piezoelectric printers,are well known in the art and will form part of the skilled person'scommon general knowledge. The printer may be a high-speed inkjetprinter. The printer is preferably a pagewidth printer. Preferred inkjetprinters and printheads for use in the present invention are describedin the following patent applications, all of which are incorporatedherein by reference in their entirety. 10/302,274 6692108 667270910/303,348 6672710 6669334 10/302,668 10/302,577 6669333 10/302,61810/302,617 10/302,297

Printhead

A Memjet printer generally has two printhead integrated circuits thatare mounted adjacent each other to form a pagewidth printhead.Typically, the printhead ICs can vary in size from 2 inches to 8 inches,so several combinations can be used to produce, say, an A4 pagewidthprinthead. For example two printhead ICs of 7 and 3 inches, 2 and 4inches, or 5 and 5 inches could be used to create an A4 printhead (thenotation is 7:3). Similarly 6 and 4 (6:4) or 5 and 5 (5:5) combinationscan be used. An A3 printhead can be constructed from 8 and 6-inchprinthead integrated circuits, for example. For photographic printing,particularly in camera, smaller printheads can be used. It will also beappreciated that a single printhead integrated circuit, or more than twosuch circuits, can also be used to achieve the required printhead width.

A preferred printhead embodiment of the pinthead will now be describedwith reference to FIGS. 17 and 18. A printhead 420 takes the form of anelongate unit. As best shown in FIG. 18, the components of the printhead420 include a support member 421, a flexible PCB 422, an inkdistribution molding 423, an ink distribution plate 424, a MEMSprinthead comprising first and second printhead integrated circuits(ICs) 425 and 426, and busbars 427.

The support member 421 is can be formed from any suitable material, suchas metal or plastic, and can be extruded, molded or formed in any otherway. The support member 421 should be strong enough to hold the othercomponents in the appropriate alignment relative to each other whilststiffening and strengthening the printhead as a whole.

The flexible PCB extends the length of the printhead 420 and includesfirst and second electrical connectors 428 and 429. The electricalconnectors 428 and 429 correspond with flexible connectors (not shown).The electrical connectors include contact areas 450 and 460 that, inuse, are positioned in contact with corresponding output connectors froma SoPEC chip (not shown). Data from the SoPEC chip passes along theelectrical connectors 428 and 429, and is distributed to respective endsof the first and second printhead ICs 425 and 426.

As shown in FIG. 19, the ink distribution molding 423 includes aplurality of elongate conduits 430 that distribute fluids (ie, coloredinks, infrared ink and fixative) and pressurized air from the air pumpalong the length of the printhead 420 (FIG. 18). Sets of fluid apertures431 (FIG. 20) disposed along the length of the ink distribution molding423 distribute the fluids and air from the conduits 430 to the inkdistribution plate 424. The fluids and air are supplied via nozzles 440formed on a plug 441 (FIG. 21), which plugs into a corresponding socket(not shown) in the printer.

The distribution plate 424 is a multi-layer construction configured totake fluids provided locally from the fluid apertures 431 and distributethem through smaller distribution apertures 432 into the printhead ICs425 and 426 (as shown in FIG. 20).

The printhead ICs 425 and 426 are positioned end to end, and are held incontact with the distribution plate 424 so that ink from the smallerdistribution apertures 432 can be fed into corresponding apertures (notshown) in the printhead ICs 425 and 426.

The busbars 427 are relatively high-capacity conductors positioned toprovide drive current to the actuators of the printhead nozzles(described in detail below). As best shown in FIG. 20, the busbars 427are retained in position at one end by a socket 433, and at both ends bywrap-around wings 434 of the flexible PCB 422. The busbars also helphold the printhead ICs 425 in position.

As shown best in FIG. 18, when assembled, the flexible PCB 422 iseffectively wrapped around the other components, thereby holding them incontact with each other. Notwithstanding this binding effect, thesupport member 421 provides a major proportion of the required stiffnessand strength of the printhead 420 as a whole.

Two forms of printhead nozzles (“thermal bend actuator” and “bubbleforming heater element actuator”), suitable for use in the printheaddescribed above, will now be described.

Thermal Bend Actuator

In the thermal bend actuator, there is typically provided a nozzlearrangement having a nozzle chamber containing ink and a thermal bendactuator connected to a paddle positioned within the chamber. Thethermal actuator device is actuated so as to eject ink from the nozzlechamber. The preferred embodiment includes a particular thermal bendactuator which includes a series of tapered portions for providingconductive heating of a conductive trace. The actuator is connected tothe paddle via an arm received through a slotted wall of the nozzlechamber. The actuator arm has a mating shape so as to mate substantiallywith the surfaces of the slot in the nozzle chamber wall.

Turning initially to FIGS. 22(a)-(c), there is provided schematicillustrations of the basic operation of a nozzle arrangement of thisembodiment. A nozzle chamber 501 is provided filled with ink 502 bymeans of an ink inlet channel 503 which can be etched through a wafersubstrate on which the nozzle chamber 501 rests. The nozzle chamber 501further includes an ink ejection port 504 around which an ink meniscusforms.

Inside the nozzle chamber 501 is a paddle type device 507 which isinterconnected to an actuator 508 through a slot in the wall of thenozzle chamber 501. The actuator 508 includes a heater means e.g. 509located adjacent to an end portion of a post 510. The post 510 is fixedto a substrate.

When it is desired to eject a drop from the nozzle chamber 501, asillustrated in FIG. 22(b), the heater means 509 is heated so as toundergo thermal expansion. Preferably, the heater means 509 itself orthe other portions of the actuator 508 are built from materials having ahigh bend efficiency where the bend efficiency is defined as:${{bend}\quad{efficiency}} = \frac{{{Young}’}s\quad{Modulus} \times \left( {{Coefficient}\quad{of}\quad{thermal}\quad{Expansion}} \right)}{{Density} \times {Specific}\quad{Heat}\quad{Capacity}}$

A suitable material for the heater elements is a copper nickel alloywhich can be formed so as to bend a glass material.

The heater means 509 is ideally located adjacent the end portion of thepost 510 such that the effects of activation are magnified at the paddleend 507 such that small thermal expansions near the post 510 result inlarge movements of the paddle end.

The heater means 509 and consequential paddle movement causes a generalincrease in pressure around the ink meniscus 505 which expands, asillustrated in FIG. 22(b), in a rapid manner. The heater current ispulsed and ink is ejected out of the port 504 in addition to flowing infrom the ink channel 503.

Subsequently, the paddle 507 is deactivated to again return to itsquiescent position. The deactivation causes a general reflow of the inkinto the nozzle chamber. The forward momentum of the ink outside thenozzle rim and the corresponding backflow results in a general neckingand breaking off of the drop 512 which proceeds to the print media. Thecollapsed meniscus 505 results in a general sucking of ink into thenozzle chamber 502 via the ink flow channel 503. In time, the nozzlechamber 501 is refilled such that the position in FIG. 22(a) is againreached and the nozzle chamber is subsequently ready for the ejection ofanother drop of ink.

FIG. 23 illustrates a side perspective view of the nozzle arrangement.FIG. 24 illustrates sectional view through an array of nozzlearrangement of FIG. 23. In these figures, the numbering of elementspreviously introduced has been retained.

Firstly, the actuator 508 includes a series of tapered actuator unitse.g. 515 which comprise an upper glass portion (amorphous silicondioxide) 516 formed on top of a titanium nitride layer 517.Alternatively a copper nickel alloy layer (hereinafter calledcupronickel) can be utilized which will have a higher bend efficiency.

The titanium nitride layer 517 is in a tapered form and, as such,resistive heating takes place near an end portion of the post 510.Adjacent titanium nitride/glass portions 515 are interconnected at ablock portion 519 which also provides a mechanical structural supportfor the actuator 508.

The heater means 509 ideally includes a plurality of the taperedactuator unit 515 which are elongate and spaced apart such that, uponheating, the bending force exhibited along the axis of the actuator 508is maximized. Slots are defined between adjacent tapered units 515 andallow for slight differential operation of each actuator 508 withrespect to adjacent actuators 508.

The block portion 519 is interconnected to an arm 520. The arm 520 is inturn connected to the paddle 507 inside the nozzle chamber 501 by meansof a slot e.g. 522 formed in the side of the nozzle chamber 501. Theslot 522 is designed generally to mate with the surfaces of the arm 520so as to minimize opportunities for the outflow of ink around the arm520. The ink is held generally within the nozzle chamber 501 via surfacetension effects around the slot 522.

When it is desired to actuate the arm 520, a conductive current ispassed through the titanium nitride layer 517 via vias within the blockportion 519 connecting to a lower CMOS layer 506 which provides thenecessary power and control circuitry for the nozzle arrangement. Theconductive current results in heating of the nitride layer 517 adjacentto the post 510 which results in a general upward bending of the arm 20and consequential ejection of ink out of the nozzle 504. The ejecteddrop is printed on a page in the usual manner for an inkjet printer aspreviously described.

An array of nozzle arrangements can be formed so as to create a singleprinthead. For example, in FIG. 24 there is illustrated a partlysectioned various array view which comprises multiple ink ejectionnozzle arrangements of FIG. 23 laid out in interleaved lines so as toform a printhead array. Of course, different types of arrays can beformulated including full color arrays etc.

The construction of the printhead system described can proceed utilizingstandard MEMS techniques through suitable modification of the steps asset out in U.S. Pat. No. 6,243,113 entitled “Image Creation Method andApparatus (IJ 41)” to the present applicant, the contents of which arefully incorporated by cross reference.

Bubble Forming Heater Element Actuator

With reference to FIG. 17, the unit cell 1001 of a bubble forming heaterelement actuator comprises a nozzle plate 1002 with nozzles 1003therein, the nozzles having nozzle rims 1004, and apertures 1005extending through the nozzle plate. The nozzle plate 1002 is plasmaetched from a silicon nitride structure which is deposited, by way ofchemical vapor deposition (CVD), over a sacrificial material which issubsequently etched.

The printhead also includes, with respect to each nozzle 1003, sidewalls 1006 on which the nozzle plate is supported, a chamber 1007defined by the walls and the nozzle plate 1002, a multi-layer substrate1008 and an inlet passage 1009 extending through the multi-layersubstrate to the far side (not shown) of the substrate. A looped,elongate heater element 1010 is suspended within the chamber 1007, sothat the element is in the form of a suspended beam. The printhead asshown is a microelectromechanical system (MEMS) structure, which isformed by a lithographic process.

When the printhead is in use, ink 1011 from a reservoir (not shown)enters the chamber 1007 via the inlet passage 1009, so that the chamberfills. Thereafter, the heater element 1010 is heated for somewhat lessthan 1 micro second, so that the heating is in the form of a thermalpulse. It will be appreciated that the heater element 1010 is in thermalcontact with the ink 1011 in the chamber 1007 so that when the elementis heated, this causes the generation of vapor bubbles in the ink.Accordingly, the ink 1011 constitutes a bubble forming liquid.

The bubble 1012, once generated, causes an increase in pressure withinthe chamber 1007, which in turn causes the ejection of a drop 1016 ofthe ink 1011 through the nozzle 1003. The rim 1004 assists in directingthe drop 1016 as it is ejected, so as to minimize the chance of a dropmisdirection.

The reason that there is only one nozzle 1003 and chamber 1007 per inletpassage 1009 is so that the pressure wave generated within the chamber,on heating of the element 1010 and forming of a bubble 1012, does noteffect adjacent chambers and their corresponding nozzles.

The increase in pressure within the chamber 1007 not only pushes ink1011 out through the nozzle 1003, but also pushes some ink back throughthe inlet passage 1009. However, the inlet passage 1009 is approximately200 to 300 microns in length, and is only approximately 16 microns indiameter. Hence there is a substantial viscous drag. As a result, thepredominant effect of the pressure rise in the chamber 1007 is to forceink out through the nozzle 1003 as an ejected drop 1016, rather thanback through the inlet passage 9.

As shown in FIG. 17, the ink drop 1016 is being ejected is shown duringits “necking phase” before the drop breaks off. At this stage, thebubble 1012 has already reached its maximum size and has then begun tocollapse towards the point of collapse 1017.

The collapsing of the bubble 1012 towards the point of collapse 1017causes some ink 1011 to be drawn from within the nozzle 1003 (from thesides 1018 of the drop), and some to be drawn from the inlet passage1009, towards the point of collapse. Most of the ink 1011 drawn in thismanner is drawn from the nozzle 1003, forming an annular neck 1019 atthe base of the drop 16 prior to its breaking off.

The drop 1016 requires a certain amount of momentum to overcome surfacetension forces, in order to break off. As ink 1011 is drawn from thenozzle 1003 by the collapse of the bubble 1012, the diameter of the neck1019 reduces thereby reducing the amount of total surface tensionholding the drop, so that the momentum of the drop as it is ejected outof the nozzle is sufficient to allow the drop to break off.

When the drop 1016 breaks off, cavitation forces are caused as reflectedby the arrows 1020, as the bubble 1012 collapses to the point ofcollapse 1017. It will be noted that there are no solid surfaces in thevicinity of the point of collapse 1017 on which the cavitation can havean effect.

Inkjet Cartridges

The inkjet ink in the method described above may be contained in an inkcartridge. Ink cartridges for inkjet printers are well known in the artand are available in numerous forms. Preferably, the inkjet inkcartridges are replaceable. Inkjet cartridges suitable for use in thepresent invention are described in the following patent applications,all of which are incorporated herein by reference in their entirety.6428155, 10/171,987In one preferred form, the ink cartridge comprises:

-   -   a housing defining a plurality of storage areas wherein at least        one of the storage areas contains colorant for printing        information that is visible to the human eye and at least one of        the other storage areas contains an inkjet ink as described        above.

Preferably, each storage area is sized corresponding to the expectedlevels of use of its contents relative to the intended print coveragefor a number of printed pages.

There now follows a brief description of a typical ink cartridge. FIG.12 shows the complete assembly of the replaceable ink cartridge 627. Ithas bladders or chambers for storing fixative 644, adhesive 630, andcyan 631, magenta 632, yellow 633, black 634 and infrared 635 inks. Thecartridge 627 also contains a micro air filter 636 in a base molding637. As shown in FIG. 9, the micro air filter 636 interfaces with an airpump 638 inside the printer via a hose 639. This provides filtered airto the printheads 705 to prevent ingress of micro particles into theMemjet™ printheads 705 which may clog the nozzles. By incorporating theair filter 636 within the cartridge 627, the operational life of thefilter is effectively linked to the life of the cartridge. This ensuresthat the filter is replaced together with the cartridge rather thanrelying on the user to clean or replace the filter at the requiredintervals. Furthermore, the adhesive and infrared ink are replenishedtogether with the visible inks and air filter thereby reducing howfrequently the printer operation is interrupted because of the depletionof a consumable material.

The cartridge 627 has a thin wall casing 640. The ink bladders 631 to635 and fixitive bladder 644 are suspended within the casing by a pin645 which hooks the cartridge together. The single glue bladder 630 isaccommodated in the base molding 637. This is a fully recyclable productwith a capacity for printing and gluing 3000 pages (1500 sheets).

Substrates

As mentioned above, the method of the present invention is especiallysuitable for use in connection with Hyperlabel™ and netpage systems.Such systems are described in detail in the patent applications listedabove, all of which are incorporated herein by reference in theirentirety.

Hence, the present invention provides a method of minimizing visiblecoloration of a substrate having an IR-absorbing dye disposed thereon,said method comprising reducing intermolecular interactions betweenadjacent dye molecules.

Preferably, the substrate comprises an interface surface. Preferably,the dye is disposed in the form of coded data suitable for use innetpage and/or Hyperlabel™ systems. For example, the coded data may beindicative of the identity of a product item. Preferably, the coded datais disposed over a substantial portion of an interface surface of thesubstrate (e.g. greater than 20%, greater than 50% or greater than 90%of the surface).

Preferably, the substrate is IR reflective so that the dye disposedthereon may be detected by a sensing device. The substrate may becomprised of any suitable material such as plastics (e.g. polyolefins,polyesters, polyamides etc.), paper, metal or combinations thereof.

For netpage applications, the substrate is preferably a paper sheet. ForHyperlabel™ applications, the substrate is preferably a tag, a label, apackaging material or a surface of a product item. Typically, tags andlabels are comprised of plastics, paper or combinations thereof.

In accordance with Hyperlabel™ applications of the invention, thesubstrate may be an interactive product item adapted for interactionwith a user via a sensing device and a computer system, the interactiveproduct item comprising:

-   -   a product item having an identity;    -   an interface surface associated with the product item and having        disposed thereon information relating to the product item and        coded data indicative of the identity of the product item,        wherein said coded data comprise an IR-absorbing dye as        described above.        Netpage and Hyperlabel™

Netpage applications of this invention are described generally in thefourth and fifth aspects of the invention above. Hyperlabel™applications of this invention are described generally in the sixth andseventh aspects of the invention above.

There now follows a detailed overview of netpage and Hyperlabel™. (Note:Memjet™ and Hyperlabel™ are trade marks of Silverbrook Research Pty Ltd,Australia). It will be appreciated that not every implementation willnecessarily embody all or even most of the specific details andextensions discussed below in relation to the basic system. However, thesystem is described in its most complete form to reduce the need forexternal reference when attempting to understand the context in whichthe preferred embodiments and aspects of the present invention operate.

In brief summary, the preferred form of the netpage system employs acomputer interface in the form of a mapped surface, that is, a physicalsurface which contains references to a map of the surface maintained ina computer system. The map references can be queried by an appropriatesensing device. Depending upon the specific implementation, the mapreferences may be encoded visibly or invisibly, and defined in such away that a local query on the mapped surface yields an unambiguous mapreference both within the map and among different maps. The computersystem can contain information about features on the mapped surface, andsuch information can be retrieved based on map references supplied by asensing device used with the mapped surface. The information thusretrieved can take the form of actions which are initiated by thecomputer system on behalf of the operator in response to the operator'sinteraction with the surface features.

In its preferred form, the netpage system relies on the production of,and human interaction with, netpages. These are pages of text, graphicsand images printed on ordinary paper, but which work like interactiveweb pages. Information is encoded on each page using ink which issubstantially invisible to the unaided human eye. The ink, however, andthereby the coded data, can be sensed by an optically imaging pen andtransmitted to the netpage system.

In the preferred form, active buttons and hyperlinks on each page can beclicked with the pen to request information from the network or tosignal preferences to a network server. In one embodiment, text writtenby hand on a netpage is automatically recognized and converted tocomputer text in the netpage system, allowing forms to be filled in. Inother embodiments, signatures recorded on a netpage are automaticallyverified, allowing e-commerce transactions to be securely authorized.

As illustrated in FIG. 1, a printed netpage 1 can represent aninteractive form which can be filled in by the user both physically, onthe printed page, and “electronically”, via communication between thepen and the netpage system. The example shows a “Request” formcontaining name and address fields and a submit button. The netpageconsists of graphic data 2 printed using visible ink, and coded data 3printed as a collection of tags 4 using invisible ink. The correspondingpage description 5, stored on the netpage network, describes theindividual elements of the netpage. In particular it describes the typeand spatial extent (zone) of each interactive element (i.e. text fieldor button in the example), to allow the netpage system to correctlyinterpret input via the netpage. The submit button 6, for example, has azone 7 which corresponds to the spatial extent of the correspondinggraphic 8.

As illustrated in FIG. 2, the netpage pen 101, a preferred form of whichis shown in FIGS. 6 and 7 and described in more detail below, works inconjunction with a personal computer (PC), Web terminal 75, or a netpageprinter 601. The netpage printer is an Internet-connected printingappliance for home, office or mobile use. The pen is wireless andcommunicates securely with the netpage network via a short-range radiolink 9. Short-range communication is relayed to the netpage network by alocal relay function which is either embedded in the PC, Web terminal ornetpage printer, or is provided by a separate relay device 44. The relayfunction can also be provided by a mobile phone or other device whichincorporates both short-range and longer-range communications functions.

In an alternative embodiment, the netpage pen utilises a wiredconnection, such as a USB or other serial connection, to the PC, Webterminal, netpage printer or relay device.

The netpage printer 601, a preferred form of which is shown in FIGS. 9to 11 and described in more detail below, is able to deliver,periodically or on demand, personalized newspapers, magazines, catalogs,brochures and other publications, all printed at high quality asinteractive netpages. Unlike a personal computer, the netpage printer isan appliance which can be, for example, wall-mounted adjacent to an areawhere the morning news is first consumed, such as in a user's kitchen,near a breakfast table, or near the household's point of departure forthe day. It also comes in tabletop, desktop, portable and miniatureversions.

Netpages printed at their point of consumption combine the ease-of-useof paper with the timeliness and interactivity of an interactive medium.

As shown in FIG. 2, the netpage pen 101 interacts with the coded data ona printed netpage 1 (or product item 201) and communicates theinteraction via a short-range radio link 9 to a relay. The relay sendsthe interaction to the relevant netpage page server 10 forinterpretation. In appropriate circumstances, the page server sends acorresponding message to application computer software running on anetpage application server 13. The application server may in turn send aresponse which is printed on the originating printer.

In an alternative embodiment, the PC, Web terminal, netpage printer orrelay device may communicate directly with local or remote applicationsoftware, including a local or remote Web server. Relatedly, output isnot limited to being printed by the netpage printer. It can also bedisplayed on the PC or Web terminal, and further interaction can bescreen-based rather than paper-based, or a mixture of the two.

The netpage system is made considerably more convenient in the preferredembodiment by being used in conjunction with high-speedmicroelectromechanical system (MEMS) based inkjet (Memjet™) printers. Inthe preferred form of this technology, relatively high-speed andhigh-quality printing is made more affordable to consumers. In itspreferred form, a netpage publication has the physical characteristicsof a traditional news-magazine, such as a set of letter-size glossypages printed in full color on both sides, bound together for easynavigation and comfortable handling.

The netpage printer exploits the growing availability of broadbandInternet access. Cable service is available to 95% of households in theUnited States, and cable modem service offering broadband Internetaccess is already available to 20% of these. The netpage printer canalso operate with slower connections, but with longer delivery times andlower image quality. Indeed, the netpage system can be enabled usingexisting consumer inkjet and laser printers, although the system willoperate more slowly and will therefore be less acceptable from aconsumer's point of view. In other embodiments, the netpage system ishosted on a private intranet. In still other embodiments, the netpagesystem is hosted on a single computer or computer-enabled device, suchas a printer.

Netpage publication servers 14 on the netpage network are configured todeliver print-quality publications to netpage printers. Periodicalpublications are delivered automatically to subscribing netpage printersvia pointcasting and multicasting Internet protocols. Personalizedpublications are filtered and formatted according to individual userprofiles.

A netpage printer can be configured to support any number of pens, and apen can work with any number of netpage printers. In the preferredimplementation, each netpage pen has a unique identifier. A householdmay have a collection of colored netpage pens, one assigned to eachmember of the family. This allows each user to maintain a distinctprofile with respect to a netpage publication server or applicationserver.

A netpage pen can also be registered with a netpage registration server11 and linked to one or more payment card accounts. This allowse-commerce payments to be securely authorized using the netpage pen. Thenetpage registration server compares the signature captured by thenetpage pen with a previously registered signature, allowing it toauthenticate the user's identity to an e-commerce server. Otherbiometrics can also be used to verify identity. A version of the netpagepen includes fingerprint scanning, verified in a similar way by thenetpage registration server.

Although a netpage printer may deliver periodicals such as the morningnewspaper without user intervention, it can be configured never todeliver unsolicited junk mail. In its preferred form, it only deliversperiodicals from subscribed or otherwise authorized sources. In thisrespect, the netpage printer is unlike a fax machine or e-mail accountwhich is visible to any junk mailer who knows the telephone number oremail address.

1 NETPAGE SYSTEM ARCHITECTURE

Each object model in the system is described using a Unified ModelingLanguage (UML) class diagram. A class diagram consists of a set ofobject classes connected by relationships, and two kinds ofrelationships are of interest here: associations and generalizations. Anassociation represents some kind of relationship between objects, i.e.between instances of classes. A generalization relates actual classes,and can be understood in the following way: if a class is thought of asthe set of all objects of that class, and class A is a generalization ofclass B, then B is simply a subset of A. The UML does not directlysupport second-order modelling—i.e. classes of classes.

Each class is drawn as a rectangle labelled with the name of the class.It contains a list of the attributes of the class, separated from thename by a horizontal line, and a list of the operations of the class,separated from the attribute list by a horizontal line. In the classdiagrams which follow, however, operations are never modelled.

An association is drawn as a line joining two classes, optionallylabelled at either end with the multiplicity of the association. Thedefault multiplicity is one. An asterisk (*) indicates a multiplicity of“many”, i.e. zero or more. Each association is optionally labelled withits name, and is also optionally labelled at either end with the role ofthe corresponding class. An open diamond indicates an aggregationassociation (“is-part-of”), and is drawn at the aggregator end of theassociation line.

A generalization relationship (“is-a”) is drawn as a solid line joiningtwo classes, with an arrow (in the form of an open triangle) at thegeneralization end.

When a class diagram is broken up into multiple diagrams, any classwhich is duplicated is shown with a dashed outline in all but the maindiagram which defines it. It is shown with attributes only where it isdefined.

1.1 Netpages

Netpages are the foundation on which a netpage network is built. Theyprovide a paper-based user interface to published information andinteractive services.

A netpage consists of a printed page (or other surface region) invisiblytagged with references to an online description of the page. The onlinepage description is maintained persistently by a netpage page server.The page description describes the visible layout and content of thepage, including text, graphics and images. It also describes the inputelements on the page, including buttons, hyperlinks, and input fields. Anetpage allows markings made with a netpage pen on its surface to besimultaneously captured and processed by the netpage system.

Multiple netpages can share the same page description. However, to allowinput through otherwise identical pages to be distinguished, eachnetpage is assigned a unique page identifier. This page ID hassufficient precision to distinguish between a very large number ofnetpages.

Each reference to the page description is encoded in a printed tag. Thetag identifies the unique page on which it appears, and therebyindirectly identifies the page description. The tag also identifies itsown position on the page. Characteristics of the tags are described inmore detail below.

Tags are printed in infrared-absorptive ink on any substrate which isinfrared-reflective, such as ordinary paper. Near-infrared wavelengthsare invisible to the human eye but are easily sensed by a solid-stateimage sensor with an appropriate filter.

A tag is sensed by an area image sensor in the netpage pen, and the tagdata is transmitted to the netpage system via the nearest netpageprinter. The pen is wireless and communicates with the netpage printervia a short-range radio link. Tags are sufficiently small and denselyarranged that the pen can reliably image at least one tag even on asingle click on the page. It is important that the pen recognize thepage ID and position on every interaction with the page, since theinteraction is stateless. Tags are error-correctably encoded to makethem partially tolerant to surface damage.

The netpage page server maintains a unique page instance for eachprinted netpage, allowing it to maintain a distinct set of user-suppliedvalues for input fields in the page description for each printednetpage.

The relationship between the page description, the page instance, andthe printed netpage is shown in FIG. 4. The printed netpage may be partof a printed netpage document 45. The page instance is associated withboth the netpage printer which printed it and, if known, the netpageuser who requested it.

As shown in FIG. 4, one or more netpages may also be associated with aphysical object such as a product item, for example when printed ontothe product item's label, packaging, or actual surface.

1.2 Netpage Tags

1.2.1 Tag Data Content

In a preferred form, each tag identifies the region in which it appears,and the location of that tag within the region. A tag may also containflags which relate to the region as a whole or to the tag. One or moreflag bits may, for example, signal a tag sensing device to providefeedback indicative of a function associated with the immediate area ofthe tag, without the sensing device having to refer to a description ofthe region. A netpage pen may, for example, illuminate an “active area”LED when in the zone of a hyperlink.

As will be more clearly explained below, in a preferred embodiment, eachtag contains an easily recognized invariant structure which aids initialdetection, and which assists in minimizing the effect of any warpinduced by the surface or by the sensing process. The tags preferablytile the entire page, and are sufficiently small and densely arrangedthat the pen can reliably image at least one tag even on a single clickon the page. It is important that the pen recognize the page ID andposition on every interaction with the page, since the interaction isstateless.

In a preferred embodiment, the region to which a tag refers coincideswith an entire page, and the region ID encoded in the tag is thereforesynonymous with the page ID of the page on which the tag appears. Inother embodiments, the region to which a tag refers can be an arbitrarysubregion of a page or other surface. For example, it can coincide withthe zone of an interactive element, in which case the region ID candirectly identify the interactive element.

In the preferred form, each tag contains 120 bits of information. Theregion ID is typically allocated up to 100 bits, the tag ID at least 16bits, and the remaining bits are allocated to flags etc. Assuming a tagdensity of 64 per square inch, a 16-bit tag ID supports a region size ofup to 1024 square inches. Larger regions can be mapped continuouslywithout increasing the tag ID precision simply by using abutting regionsand maps. The 100-bit region ID allows 2¹⁰⁰ (˜10³⁰ or a million trilliontrillion) different regions to be uniquely identified.

1.2.2 Tag Data Encoding

In one embodiment, the 120 bits of tag data are redundantly encodedusing a (15, 5) Reed-Solomon code. This yields 360 encoded bitsconsisting of 6 codewords of 15 4-bit symbols each. The (15, 5) codeallows up to 5 symbol errors to be corrected per codeword, i.e. it istolerant of a symbol error rate of up to 33% per codeword.

Each 4-bit symbol is represented in a spatially coherent way in the tag,and the symbols of the six codewords are interleaved spatially withinthe tag. This ensures that a burst error (an error affecting multiplespatially adjacent bits) damages a minimum number of symbols overall anda minimum number of symbols in any one codeword, thus maximising thelikelihood that the burst error can be fully corrected.

Any suitable error-correcting code code can be used in place of a (15,5) Reed-Solomon code, for example: a Reed-Solomon code with more or lessredundancy, with the same or different symbol and codeword sizes;another block code; or a different kind of code, such as a convolutionalcode (see, for example, Stephen B. Wicker, Error Control Systems forDigital Communication and Storage, Prentice-Hall 1995, the contents ofwhich a herein incorporated by reference thereto).

In order to support “single-click” interaction with a tagged region viaa sensing device, the sensing device must be able to see at least oneentire tag in its field of view no matter where in the region or at whatorientation it is positioned. The required diameter of the field of viewof the sensing device is therefore a function of the size and spacing ofthe tags.

1.2.3 Tag Structure

FIG. 5 a shows a tag 4, in the form of tag 726 with four perspectivetargets 17. The tag 726 represents sixty 4-bit Reed-Solomon symbols 747,for a total of 240 bits. The tag represents each “one” bit by thepresence of a mark 748, referred to as a macrodot, and each “zero” bitby the absence of the corresponding macrodot. FIG. 5 c shows a squaretiling 728 of nine tags, containing all “one” bits for illustrativepurposes. It will be noted that the perspective targets are designed tobe shared between adjacent tags. FIG. 5 d shows a square tiling of 16tags and a corresponding minimum field of view 193, which spans thediagonals of two tags.

Using a (15, 7) Reed-Solomon code, 112 bits of tag data are redundantlyencoded to produce 240 encoded bits. The four codewords are interleavedspatially within the tag to maximize resilience to burst errors.Assuming a 16-bit tag ID as before, this allows a region ID of up to 92bits.

The data-bearing macrodots 748 of the tag are designed to not overlaptheir neighbors, so that groups of tags cannot produce structures thatresemble targets. This also saves ink. The perspective targets allowdetection of the tag, so further targets are not required.

Although the tag may contain an orientation feature to allowdisambiguation of the four possible orientations of the tag relative tothe sensor, the present invention is concerned with embeddingorientation data in the tag data. For example, the four codewords can bearranged so that each tag orientation (in a rotational sense) containsone codeword placed at that orientation, as shown in FIG. 5 a, whereeach symbol is labelled with the number of its codeword (1-4) and theposition of the symbol within the codeword (A-O). Tag decoding thenconsists of decoding one codeword at each rotational orientation. Eachcodeword can either contain a single bit indicating whether it is thefirst codeword, or two bits indicating which codeword it is. The latterapproach has the advantage that if, say, the data content of only onecodeword is required, then at most two codewords need to be decoded toobtain the desired data. This may be the case if the region ID is notexpected to change within a stroke and is thus only decoded at the startof a stroke. Within a stroke only the codeword containing the tag ID isthen desired. Furthermore, since the rotation of the sensing devicechanges slowly and predictably within a stroke, only one codewordtypically needs to be decoded per frame.

It is possible to dispense with perspective targets altogether andinstead rely on the data representation being self-registering. In thiscase each bit value (or multi-bit value) is typically represented by anexplicit glyph, i.e. no bit value is represented by the absence of aglyph. This ensures that the data grid is well-populated, and thusallows the grid to be reliably identified and its perspective distortiondetected and subsequently corrected during data sampling. To allow tagboundaries to be detected, each tag data must contain a marker pattern,and these must be redundantly encoded to allow reliable detection. Theoverhead of such marker patterns is similar to the overhead of explicitperspective targets. Various such schemes are described in the presentapplicants' co-pending PCT application PCT/AU01/01274 filed 11 Oct.2001.

The arrangement 728 of FIG. 5 c shows that the square tag 726 can beused to fully tile or tesselate, i.e. without gaps or overlap, a planeof arbitrary size.

Although in preferred embodiments the tagging schemes described hereinencode a single data bit using the presence or absence of a singleundifferentiated macrodot, they can also use sets of differentiatedglyphs to represent single-bit or multi-bit values, such as the sets ofglyphs illustrated in the present applicants' co-pending PCT applicationPCT/AU01/01274 filed 11 Oct. 2001.

1.3 The Netpage Network

In a preferred embodiment, a netpage network consists of a distributedset of netpage page servers 10, netpage registration servers 11, netpageID servers 12, netpage application servers 13, netpage publicationservers 14, Web terminals 75, netpage printers 601, and relay devices 44connected via a network 19 such as the Internet, as shown in FIG. 3.

The netpage registration server 11 is a server which recordsrelationships between users, pens, printers, applications andpublications, and thereby authorizes various network activities. Itauthenticates users and acts as a signing proxy on behalf ofauthenticated users in application transactions. It also provideshandwriting recognition services. As described above, a netpage pageserver 10 maintains persistent information about page descriptions andpage instances. The netpage network includes any number of page servers,each handling a subset of page instances. Since a page server alsomaintains user input values for each page instance, clients such asnetpage printers send netpage input directly to the appropriate pageserver. The page server interprets any such input relative to thedescription of the corresponding page.

A netpage ID server 12 allocates document IDs 51 on demand, and providesload-balancing of page servers via its ID allocation scheme.

A netpage printer uses the Internet Distributed Name System (DNS), orsimilar, to resolve a netpage page ID 50 into the network address of thenetpage page server handling the corresponding page instance.

A netpage application server 13 is a server which hosts interactivenetpage applications. A netpage publication server 14 is an applicationserver which publishes netpage documents to netpage printers.

Netpage servers can be hosted on a variety of network server platformsfrom manufacturers such as IBM, Hewlett-Packard, and Sun. Multiplenetpage servers can run concurrently on a single host, and a singleserver can be distributed over a number of hosts. Some or all of thefunctionality provided by netpage servers, and in particular thefunctionality provided by the ID server and the page server, can also beprovided directly in a netpage appliance such as a netpage printer, in acomputer workstation, or on a local network.

1.4 The Netpage Printer

The netpage printer 601 is an appliance which is registered with thenetpage system and prints netpage documents on demand and viasubscription. Each printer has a unique printer ID 62, and is connectedto the netpage network via a network such as the Internet, ideally via abroadband connection.

Apart from identity and security settings in non-volatile memory, thenetpage printer contains no persistent storage. As far as a user isconcerned, “the network is the computer”. Netpages functioninteractively across space and time with the help of the distributednetpage page servers 10, independently of particular netpage printers.

The netpage printer receives subscribed netpage documents from netpagepublication servers 14. Each document is distributed in two parts: thepage layouts, and the actual text and image objects which populate thepages. Because of personalization, page layouts are typically specificto a particular subscriber and so are pointcast to the subscriber'sprinter via the appropriate page server. Text and image objects, on theother hand, are typically shared with other subscribers, and so aremulticast to all subscribers' printers and the appropriate page servers.

The netpage publication server optimizes the segmentation of documentcontent into pointcasts and multicasts. After receiving the pointcast ofa document's page layouts, the printer knows which multicasts, if any,to listen to.

Once the printer has received the complete page layouts and objects thatdefine the document to be printed, it can print the document.

The printer rasterizes and prints odd and even pages simultaneously onboth sides of the sheet. It contains duplexed print engine controllers760 and print engines utilizing Memjet™ printheads 350 for this purpose.

The printing process consists of two decoupled stages: rasterization ofpage descriptions, and expansion and printing of page images. The rasterimage processor (RIP) consists of one or more standard DSPs 757 runningin parallel. The duplexed print engine controllers consist of customprocessors which expand, dither and print page images in real time,synchronized with the operation of the printheads in the print engines.

Printers not enabled for IR printing have the option to print tags usingIR-absorptive black ink, although this restricts tags to otherwise emptyareas of the page. Although such pages have more limited functionalitythan IR-printed pages, they are still classed as netpages.

A normal netpage printer prints netpages on sheets of paper. Morespecialised netpage printers may print onto more specialised surfaces,such as globes. Each printer supports at least one surface type, andsupports at least one tag tiling scheme, and hence tag map, for eachsurface type. The tag map 811 which describes the tag tiling schemeactually used to print a document becomes associated with that documentso that the document's tags can be correctly interpreted.

FIG. 2 shows the netpage printer class diagram, reflectingprinter-related information maintained by a registration server 11 onthe netpage network.

1.5 The Netpage Pen

The active sensing device of the netpage system is typically a pen 101,which, using its embedded controller 134, is able to capture and decodeIR position tags from a page via an image sensor. The image sensor is asolid-state device provided with an appropriate filter to permit sensingat only near-infrared wavelengths. As described in more detail below,the system is able to sense when the nib is in contact with the surface,and the pen is able to sense tags at a sufficient rate to capture humanhandwriting (i.e. at 200 dpi or greater and 100 Hz or faster).Information captured by the pen is encrypted and wirelessly transmittedto the printer (or base station), the printer or base stationinterpreting the data with respect to the (known) page structure.

The preferred embodiment of the netpage pen operates both as a normalmarking ink pen and as a non-marking stylus. The marking aspect,however, is not necessary for using the netpage system as a browsingsystem, such as when it is used as an Internet interface. Each netpagepen is registered with the netpage system and has a unique pen ID 61.FIG. 14 shows the netpage pen class diagram, reflecting pen-relatedinformation maintained by a registration server 11 on the netpagenetwork.

When either nib is in contact with a netpage, the pen determines itsposition and orientation relative to the page. The nib is attached to aforce sensor, and the force on the nib is interpreted relative to athreshold to indicate whether the pen is “up” or “down”. This allows ainteractive element on the page to be ‘clicked’ by pressing with the pennib, in order to request, say, information from a network. Furthermore,the force is captured as a continuous value to allow, say, the fulldynamics of a signature to be verified.

The pen determines the position and orientation of its nib on thenetpage by imaging, in the infrared spectrum, an area 193 of the page inthe vicinity of the nib. It decodes the nearest tag and computes theposition of the nib relative to the tag from the observed perspectivedistortion on the imaged tag and the known geometry of the pen optics.Although the position resolution of the tag may be low, because the tagdensity on the page is inversely proportional to the tag size, theadjusted position resolution is quite high, exceeding the minimumresolution required for accurate handwriting recognition.

Pen actions relative to a netpage are captured as a series of strokes. Astroke consists of a sequence of time-stamped pen positions on the page,initiated by a pen-down event and completed by the subsequent pen-upevent. A stroke is also tagged with the page ID 50 of the netpagewhenever the page ID changes, which, under normal circumstances, is atthe commencement of the stroke.

Each netpage pen has a current selection 826 associated with it,allowing the user to perform copy and paste operations etc. Theselection is timestamped to allow the system to discard it after adefined time period. The current selection describes a region of a pageinstance. It consists of the most recent digital ink stroke capturedthrough the pen relative to the background area of the page. It isinterpreted in an application-specific manner once it is submitted to anapplication via a selection hyperlink activation.

Each pen has a current nib 824. This is the nib last notified by the pento the system. In the case of the default netpage pen described above,either the marking black ink nib or the non-marking stylus nib iscurrent. Each pen also has a current nib style 825. This is the nibstyle last associated with the pen by an application, e.g. in responseto the user selecting a color from a palette. The default nib style isthe nib style associated with the current nib. Strokes captured througha pen are tagged with the current nib style. When the strokes aresubsequently reproduced, they are reproduced in the nib style with whichthey are tagged.

Whenever the pen is within range of a printer with which it cancommunicate, the pen slowly flashes its “online” LED. When the pen failsto decode a stroke relative to the page, it momentarily activates its“error” LED. When the pen succeeds in decoding a stroke relative to thepage, it momentarily activates its “ok” LED.

A sequence of captured strokes is referred to as digital ink. Digitalink forms the basis for the digital exchange of drawings andhandwriting, for online recognition of handwriting, and for onlineverification of signatures.

The pen is wireless and transmits digital ink to the netpage printer viaa short-range radio link. The transmitted digital ink is encrypted forprivacy and security and packetized for efficient transmission, but isalways flushed on a pen-up event to ensure timely handling in theprinter.

When the pen is out-of-range of a printer it buffers digital ink ininternal memory, which has a capacity of over ten minutes of continuoushandwriting. When the pen is once again within range of a printer, ittransfers any buffered digital ink.

A pen can be registered with any number of printers, but because allstate data resides in netpages both on paper and on the network, it islargely immaterial which printer a pen is communicating with at anyparticular time.

A preferred embodiment of the pen is described in greater detail below,with reference to FIGS. 6 to 8.

1.6 Netpage Interaction

The netpage printer 601 receives data relating to a stroke from the pen101 when the pen is used to interact with a netpage 1. The coded data 3of the tags 4 is read by the pen when it is used to execute a movement,such as a stroke. The data allows the identity of the particular pageand associated interactive element to be determined and an indication ofthe relative positioning of the pen relative to the page to be obtained.The indicating data is transmitted to the printer, where it resolves,via the DNS, the page ID 50 of the stroke into the network address ofthe netpage page server 10 which maintains the corresponding pageinstance 830. It then transmits the stroke to the page server. If thepage was recently identified in an earlier stroke, then the printer mayalready have the address of the relevant page server in its cache. Eachnetpage consists of a compact page layout maintained persistently by anetpage page server (see below). The page layout refers to objects suchas images, fonts and pieces of text, typically stored elsewhere on thenetpage network.

When the page server receives the stroke from the pen, it retrieves thepage description to which the stroke applies, and determines whichelement of the page description the stroke intersects. It is then ableto interpret the stroke in the context of the type of the relevantelement.

A “click” is a stroke where the distance and time between the pen downposition and the subsequent pen up position are both less than somesmall maximum. An object which is activated by a click typicallyrequires a click to be activated, and accordingly, a longer stroke isignored. The failure of a pen action, such as a “sloppy” click, toregister is indicated by the lack of response from the pen's “ok” LED.

There are two kinds of input elements in a netpage page description:hyperlinks and form fields. Input through a form field can also triggerthe activation of an associated hyperlink.

2 Netpage Pen Description

2.1 Pen Mechanics

Referring to FIGS. 6 and 7, the pen, generally designated by referencenumeral 101, includes a housing 102 in the form of a plastics mouldinghaving walls 103 defining an interior space 104 for mounting the pencomponents. The pen top 105 is in operation rotatably mounted at one end106 of the housing 102. A semi-transparent cover 107 is secured to theopposite end 108 of the housing 102. The cover 107 is also of mouldedplastics, and is formed from semi-transparent material in order toenable the user to view the status of the LED mounted within the housing102. The cover 107 includes a main part 109 which substantiallysurrounds the end 108 of the housing 102 and a projecting portion 110which projects back from the main part 109 and fits within acorresponding slot 111 formed in the walls 103 of the housing 102. Aradio antenna 112 is mounted behind the projecting portion 110, withinthe housing 102. Screw threads 113 surrounding an aperture 113A on thecover 107 are arranged to receive a metal end piece 114, includingcorresponding screw threads 115. The metal end piece 114 is removable toenable ink cartridge replacement.

Also mounted within the cover 107 is a tri-color status LED 116 on aflex PCB 117. The antenna 112 is also mounted on the flex PCB 117. Thestatus LED 116 is mounted at the top of the pen 101 for good all-aroundvisibility.

The pen can operate both as a normal marking ink pen and as anon-marking stylus. An ink pen cartridge 118 with nib 119 and a stylus120 with stylus nib 121 are mounted side by side within the housing 102.Either the ink cartridge nib 119 or the stylus nib 121 can be broughtforward through open end 122 of the metal end piece 114, by rotation ofthe pen top 105. Respective slider blocks 123 and 124 are mounted to theink cartridge 118 and stylus 120, respectively. A rotatable cam barrel125 is secured to the pen top 105 in operation and arranged to rotatetherewith The cam barrel 125 includes a cam 126 in the form of a slotwithin the walls 181 of the cam barrel. Cam followers 127 and 128projecting from slider blocks 123 and 124 fit within the cam slot 126.On rotation of the cam barrel 125, the slider blocks 123 or 124 moverelative to each other to project either the pen nib 119 or stylus nib121 out through the hole 122 in the metal end piece 114. The pen 101 hasthree states of operation. By turning the top 105 through 90° steps, thethree states are:

-   -   stylus 120 nib 121 out    -   ink cartridge 118 nib 119 out, and    -   neither ink cartridge 118 nib 119 out nor stylus 120 nib 121 out

A second flex PCB 129, is mounted on an electronics chassis 130 whichsits within the housing 102. The second flex PCB 129 mounts an infraredLED 131 for providing infrared radiation for projection onto thesurface. An image sensor 132 is provided mounted on the second flex PCB129 for receiving reflected radiation from the surface. The second flexPCB 129 also mounts a radio frequency chip 133, which includes an RFtransmitter and RF receiver, and a controller chip 134 for controllingoperation of the pen 101. An optics block 135 (formed from moulded clearplastics) sits within the cover 107 and projects an infrared beam ontothe surface and receives images onto the image sensor 132. Power supplywires 136 connect the components on the second flex PCB 129 to batterycontacts 137 which are mounted within the cam barrel 125. A terminal 138connects to the battery contacts 137 and the cam barrel 125. A threevolt rechargeable battery 139 sits within the cam barrel 125 in contactwith the battery contacts. An induction charging coil 140 is mountedabout the second flex PCB 129 to enable recharging of the battery 139via induction. The second flex PCB 129 also mounts an infrared LED 143and infrared photodiode 144 for detecting displacement in the cam barrel125 when either the stylus 120 or the ink cartridge 118 is used forwriting, in order to enable a determination of the force being appliedto the surface by the pen nib 119 or stylus nib 121. The IR photodiode144 detects light from the IR LED 143 via reflectors (not shown) mountedon the slider blocks 123 and 124.

Rubber grip pads 141 and 142 are provided towards the end 108 of thehousing 102 to assist gripping the pen 101, and top 105 also includes aclip 142 for clipping the pen 101 to a pocket.

3.2 Pen Controller

The pen 101 is arranged to determine the position of its nib (stylus nib121 or ink cartridge nib 119) by imaging, in the infrared spectrum, anarea of the surface in the vicinity of the nib. It records the locationdata from the nearest location tag, and is arranged to calculate thedistance of the nib 121 or 119 from the location tab utilising optics135 and controller chip 134. The controller chip 134 calculates theorientation of the pen and the nib-to-tag distance from the perspectivedistortion observed on the imaged tag.

Utilising the RF chip 133 and antenna 112 the pen 101 can transmit thedigital ink data (which is encrypted for security and packaged forefficient transmission) to the computing system.

When the pen is in range of a receiver, the digital ink data istransmitted as it is formed. When the pen 101 moves out of range,digital ink data is buffered within the pen 101 (the pen 101 circuitryincludes a buffer arranged to store digital ink data for approximately12 minutes of the pen motion on the surface) and can be transmittedlater.

The controller chip 134 is mounted on the second flex PCB 129 in the pen101. FIG. 8 is a block diagram illustrating in more detail thearchitecture of the controller chip 134. FIG. 8 also showsrepresentations of the RF chip 133, the image sensor 132, the tri-colorstatus LED 116, the IR illumination LED 131, the IR force sensor LED143, and the force sensor photodiode 144.

The pen controller chip 134 includes a controlling processor 145. Bus146 enables the exchange of data between components of the controllerchip 134. Flash memory 147 and a 512 KB DRAM 148 are also included. Ananalog-to-digital converter 149 is arranged to convert the analog signalfrom the force sensor photodiode 144 to a digital signal.

An image sensor interface 152 interfaces with the image sensor 132. Atransceiver controller 153 and base band circuit 154 are also includedto interface with the RF chip 133 which includes an RF circuit 155 andRF resonators and inductors 156 connected to the antenna 112.

The controlling processor 145 captures and decodes location data fromtags from the surface via the image sensor 132, monitors the forcesensor photodiode 144, controls the LEDs 116, 131 and 143, and handlesshort-range radio communication via the radio transceiver 153. It is amedium-performance (˜40 MHz) general-purpose RISC processor.

The processor 145, digital transceiver components (transceivercontroller 153 and baseband circuit 154), image sensor interface 152,flash memory 147 and 512 KB DRAM 148 are integrated in a singlecontroller ASIC. Analog RF components (RF circuit 155 and RF resonatorsand inductors 156) are provided in the separate RF chip.

The image sensor is a CCD or CMOS image sensor. Depending on taggingscheme, it has a size ranging from about 100×100 pixels to 200×200pixels. Many miniature CMOS image sensors are commercially available,including the National Semiconductor LM9630.

The controller ASIC 134 enters a quiescent state after a period ofinactivity when the pen 101 is not in contact with a surface. Itincorporates a dedicated circuit 150 which monitors the force sensorphotodiode 144 and wakes up the controller 134 via the power manager 151on a pen-down event.

The radio transceiver communicates in the unlicensed 900 MHz bandnormally used by cordless telephones, or alternatively in the unlicensed2.4 GHz industrial, scientific and medical (ISM) band, and usesfrequency hopping and collision detection to provide interference-freecommunication.

In an alternative embodiment, the pen incorporates an Infrared DataAssociation (IrDA) interface for short-range communication with a basestation or netpage printer.

In a further embodiment, the pen 101 includes a pair of orthogonalaccelerometers mounted in the normal plane of the pen 101 axis. Theaccelerometers 190 are shown in FIGS. 7 and 8 in ghost outline.

The provision of the accelerometers enables this embodiment of the pen101 to sense motion without reference to surface location tags, allowingthe location tags to be sampled at a lower rate. Each location tag IDcan then identify an object of interest rather than a position on thesurface. For example, if the object is a user interface input element(e.g. a command button), then the tag ID of each location tag within thearea of the input element can directly identify the input element.

The acceleration measured by the accelerometers in each of the x and ydirections is integrated with respect to time to produce aninstantaneous velocity and position.

Since the starting position of the stroke is not known, only relativepositions within a stroke are calculated. Although position integrationaccumulates errors in the sensed acceleration, accelerometers typicallyhave high resolution, and the time duration of a stroke, over whicherrors accumulate, is short.

3 Netpage Printer Description

3.1 Printer Mechanics

The vertically-mounted netpage wallprinter 601 is shown fully assembledin FIG. 9. It prints netpages on Letter/A4 sized media using duplexed8½″ Memjet™ print engines 602 and 603, as shown in FIGS. 10 and 10 a. Ituses a straight paper path with the paper 604 passing through theduplexed print engines 602 and 603 which print both sides of a sheetsimultaneously, in full color and with full bleed.

An integral binding assembly 605 applies a strip of glue along one edgeof each printed sheet, allowing it to adhere to the previous sheet whenpressed against it. This creates a final bound document 618 which canrange in thickness from one sheet to several hundred sheets.

The replaceable ink cartridge 627, shown in FIG. 12 coupled with theduplexed print engines, has bladders or chambers for storing fixative,adhesive, and cyan, magenta, yellow, black and infrared inks. Thecartridge also contains a micro air filter in a base molding. The microair filter interfaces with an air pump 638 inside the printer via a hose639. This provides filtered air to the printheads to prevent ingress ofmicro particles into the Memjet™ printheads 350 which might otherwiseclog the printhead nozzles. By incorporating the air filter within thecartridge, the operational life of the filter is effectively linked tothe life of the cartridge. The ink cartridge is a fully recyclableproduct with a capacity for printing and gluing 3000 pages (1500sheets).

Referring to FIG. 10, the motorized media pick-up roller assembly 626pushes the top sheet directly from the media tray past a paper sensor onthe first print engine 602 into the duplexed Memjet™ printhead assembly.The two Memjet™ print engines 602 and 603 are mounted in an opposingin-line sequential configuration along the straight paper path. Thepaper 604 is drawn into the first print engine 602 by integral, poweredpick-up rollers 626. The position and size of the paper 604 is sensedand full bleed printing commences. Fixative is printed simultaneously toaid drying in the shortest possible time.

The paper exits the first Memjet™ print engine 602 through a set ofpowered exit spike wheels (aligned along the straight paper path), whichact against a rubberized roller. These spike wheels contact the ‘wet’printed surface and continue to feed the sheet 604 into the secondMemjet™ print engine 603.

Referring to FIGS. 10 and 10 a, the paper 604 passes from the duplexedprint engines 602 and 603 into the binder assembly 605. The printed pagepasses between a powered spike wheel axle 670 with a fibrous supportroller and another movable axle with spike wheels and a momentary actionglue wheel. The movable axle/glue assembly 673 is mounted to a metalsupport bracket and it is transported forward to interface with thepowered axle 670 via gears by action of a camshaft. A separate motorpowers this camshaft.

The glue wheel assembly 673 consists of a partially hollow axle 679 witha rotating coupling for the glue supply hose 641 from the ink cartridge627. This axle 679 connects to a glue wheel, which absorbs adhesive bycapillary action through radial holes. A molded housing 682 surroundsthe glue wheel, with an opening at the front. Pivoting side moldings andsprung outer doors are attached to the metal bracket and hinge outsideways when the rest of the assembly 673 is thrust forward. Thisaction exposes the glue wheel through the front of the molded housing682. Tension springs close the assembly and effectively cap the gluewheel during periods of inactivity.

As the sheet 604 passes into the glue wheel assembly 673, adhesive isapplied to one vertical edge on the front side (apart from the firstsheet of a document) as it is transported down into the binding assembly605.

4 Product Tagging

Automatic identification refers to the use of technologies such as barcodes, magnetic stripe cards, smartcards, and RF transponders, to(semi-)automatically identify objects to data processing systems withoutmanual keying.

For the purposes of automatic identification, a product item is commonlyidentified by a 12-digit Universal Product Code (UPC), encodedmachine-readably in the form of a printed bar code. The most common UPCnumbering system incorporates a 5-digit manufacturer number and a5-digit item number. Because of its limited precision, a UPC is used toidentify a class of product rather than an individual product item. TheUniform Code Council and EAN International define and administer the UPCand related codes as subsets of the 14-digit Global Trade Item Number(GTIN).

Within supply chain management, there is considerable interest inexpanding or replacing the UPC scheme to allow individual product itemsto be uniquely identified and thereby tracked. Individual item taggingcan reduce “shrinkage” due to lost, stolen or spoiled goods, improve theefficiency of demand-driven manufacturing and supply, facilitate theprofiling of product usage, and improve the customer experience.

There are two main contenders for individual item tagging: optical tagsin the form of so-called two-dimensional bar codes, and radio frequencyidentification (RFID) tags. For a detailed description of RFID tags,refer to Klaus Finkenzeller, RFID Handbook, John Wiley & Son (1999), thecontents of which are herein incorporated by cross-reference. Opticaltags have the advantage of being inexpensive, but require opticalline-of-sight for reading. RFID tags have the advantage of supportingomnidirectional reading, but are comparatively expensive. The presenceof metal or liquid can seriously interfere with RFID tag performance,undermining the omnidirectional reading advantage. Passive(reader-powered) RFID tags are projected to be priced at 10 cents eachin multi-million quantities by the end of 2003, and at 5 cents each soonthereafter, but this still falls short of the sub-one-cent industrytarget for low-price items such as grocery. The read-only nature of mostoptical tags has also been cited as a disadvantage, since status changescannot be written to a tag as an item progresses through the supplychain. However, this disadvantage is mitigated by the fact that aread-only tag can refer to information maintained dynamically on anetwork.

The Massachusetts Institute of Technology (MIT) Auto-ID Center hasdeveloped a standard for a 96-bit Electronic Product Code (EPC), coupledwith an Internet-based Object Name Service (ONS) and a Product MarkupLanguage (PML). Once an EPC is scanned or otherwise obtained, it is usedto look up, possibly via the ONS, matching product information portablyencoded in PML. The EPC consists of an 8-bit header, a 28-bit EPCmanager, a 24-bit object class, and a 36-bit serial number. For adetailed description of the EPC, refer to Brock, D. L., The ElectronicProduct Code (EPC), MIT Auto-ID Center (January 2001), the contents ofwhich are herein incorporated by cross-reference. The Auto-ID Center hasdefined a mapping of the GTIN onto the EPC to demonstrate compatibilitybetween the EPC and current practices Brock, D. L., Integrating theElectronic Product Code (EPC) and the Global Trade Item Number (GTIN),MIT Auto-ID Center (November 2001), the contents of which are hereinincorporated by cross-reference. The EPC is administered by EPCglobal,an EAN-UCC joint venture.

EPCs are technology-neutral and can be encoded and carried in manyforms. The Auto-ID Center strongly advocates the use of low-cost passiveRFID tags to carry EPCs, and has defined a 64-bit version of the EPC toallow the cost of RFID tags to be minimized in the short term. Fordetailed description of low-cost RFID tag characteristics, refer toSarma, S., Towards the 5c Tag, MIT Auto-ID Center (November 2001), thecontents of which are herein incorporated by cross-reference. For adescription of a commercially-available low-cost passive RFID tag, referto 915 MHz RFID Tag, Alien Technology (2002), the contents of which areherein incorporated by cross-reference. For detailed description of the64-bit EPC, refer to Brock, D. L., The Compact Electronic Product Code,MIT Auto-ID Center (November 2001), the contents of which are hereinincorporated by cross-reference.

EPCs are intended not just for unique item-level tagging and tracking,but also for case-level and pallet-level tagging, and for tagging ofother logistic units of shipping and transportation such as containersand trucks. The distributed PML database records dynamic relationshipsbetween items and higher-level containers in the packaging, shipping andtransportation hierarchy.

4.1 Omnitagging in the Supply Chain

Using an invisible (e.g. infrared) tagging scheme to uniquely identify aproduct item has the significant advantage that it allows the entiresurface of a product to be tagged, or a significant portion thereof,without impinging on the graphic design of the product's packaging orlabelling. If the entire product surface is tagged, then the orientationof the product doesn't affect its ability to be scanned, i.e. asignificant part of the line-of-sight disadvantage of a visible bar codeis eliminated. Furthermore, since the tags are small and massivelyreplicated, label damage no longer prevents scanning.

Omnitagging, then, consists of covering a large proportion of thesurface of a product item with optically-readable invisible tags. Eachomnitag uniquely identifies the product item on which it appears. Theomnitag may directly encode the product code (e.g. EPC) of the item, ormay encode a surrogate ID which in turn identifies the product code viaa database lookup. Each omnitag also optionally identifies its ownposition on the surface of the product item, to provide the downstreamconsumer benefits of netpage interactivity described earlier.

Omnitags are applied during product manufacture and/or packaging usingdigital printers. These may be add-on infrared printers which print theomnitags after the text and graphics have been printed by other means,or integrated color and infrared printers which print the omnitags, textand graphics simultaneously. Digitally-printed text and graphics mayinclude everything on the label or packaging, or may consist only of thevariable portions, with other portions still printed by other means.

4.2 Omnitagging

As shown in FIG. 13, a product's unique item ID 215 may be seen as aspecial kind of unique object ID 210. The Electronic Product Code (EPC)220 is one emerging standard for an item ID. An item ID typicallyconsists of a product ID 214 and a serial number 213. The product IDidentifies a class of product, while the serial number identifies aparticular instance of that class, i.e. an individual product item. Theproduct ID in turn typically consists of a manufacturer number 211 and aproduct class number 212. The best-known product ID is the EAN.UCCUniversal Product Code (UPC) 221 and its variants.

As shown in FIG. 14, an omnitag 202 encodes a page ID (or region ID) 50and a two-dimensional (2D) position 86. The region ID identifies thesurface region containing the tag, and the position identifies the tag'sposition within the two-dimensional region. Since the surface inquestion is the surface of a physical product item 201, it is useful todefine a one-to-one mapping between the region ID and the unique objectID 210, and more specifically the item ID 215, of the product item.Note, however, that the mapping can be many-to-one without compromisingthe utility of the omnitag. For example, each panel of a product item'spackaging could have a different region ID 50. Conversely, the omnitagmay directly encode the item ID, in which case the region ID containsthe item ID, suitably prefixed to decouple item ID allocation fromgeneral netpage region ID allocation. Note that the region ID uniquelydistinguishes the corresponding surface region from all other surfaceregions identified within the global netpage system.

The item ID 215 is preferably the EPC 220 proposed by the Auto-IDCenter, since this provides direct compatibility between omnitags andEPC-carrying RFID tags.

In FIG. 14 the position 86 is shown as optional. This is to indicatethat much of the utility of the omnitag in the supply chain derives fromthe region ID 50, and the position may be omitted if not desired for aparticular product.

For interoperability with the netpage system, an omnitag 202 is anetpage tag 4, i.e. it has the logical structure, physical layout andsemantics of a netpage tag.

When a netpage sensing device such as the netpage pen 101 images anddecodes an omnitag, it uses the position and orientation of the tag inits field of view and combines this with the position encoded in the tagto compute its own position relative to the tag. As the sensing deviceis moved relative to a Hyperlabelled surface region, it is thereby ableto track its own motion relative to the region and generate a set oftimestamped position samples representative of its time-varying path.When the sensing device is a pen, then the path consists of a sequenceof strokes, with each stroke starting when the pen makes contact withthe surface, and ending when the pen breaks contact with the surface.

When a stroke is forwarded to the page server 10 responsible for theregion ID, the server retrieves a description of the region keyed byregion ID, and interprets the stroke in relation to the description. Forexample, if the description includes a hyperlink and the strokeintersects the zone of the hyperlink, then the server may interpret thestroke as a designation of the hyperlink and activate the hyperlink.

4.3 Omnitag Printing

An omnitag printer is a digital printer which prints omnitags onto thelabel, packaging or actual surface of a product before, during or afterproduct manufacture and/or assembly. It is a special case of a netpageprinter 601. It is capable of printing a continuous pattern of omnitagsonto a surface, typically using a near-infrared-absorptive ink. Inhigh-speed environments, the printer includes hardware which acceleratestag rendering. This typically includes real-time Reed-Solomon encodingof variable tag data such as tag position, and real-time template-basedrendering of the actual tag pattern at the dot resolution of theprinthead.

The printer may be an add-on infrared printer which prints the omnitagsafter text and graphics have been printed by other means, or anintegrated color and infrared printer which prints the omnitags, textand graphics simultaneously. Digitally-printed text and graphics mayinclude everything on the label or packaging, or may consist only of thevariable portions, with other portions still printed by other means.Thus an omnitag printer with an infrared and black printing capabilitycan displace an existing digital printer used for variable dataprinting, such as a conventional thermal transfer or inkjet printer.

For the purposes of the following discussion, any reference to printingonto an item label is intended to include printing onto the itempackaging in general, or directly onto the item surface. Furthermore,any reference to an item ID 215 is intended to include a region ID 50(or collection of per-panel region ids), or a component thereof.

The printer is typically controlled by a host computer, which suppliesthe printer with fixed and/or variable text and graphics as well as itemids for inclusion in the omnitags. The host may provide real-timecontrol over the printer, whereby it provides the printer with data inreal time as printing proceeds. As an optimisation, the host may providethe printer with fixed data before printing begins, and only providevariable data in real time. The printer may also be capable ofgenerating per-item variable data based on parameters provided by thehost. For example, the host may provide the printer with a base item IDprior to printing, and the printer may simply increment the base item IDto generate successive item ids. Alternatively, memory in the inkcartridge or other storage medium inserted into the printer may providea source of unique item ids, in which case the printer reports theassignment of items ids to the host computer for recording by the host.

Alternatively still, the printer may be capable of reading apre-existing item ID from the label onto which the omnitags are beingprinted, assuming the unique ID has been applied in some form to thelabel during a previous manufacturing step. For example, the item ID mayalready be present in the form of a visible 2D bar code, or encoded inan RFID tag. In the former case the printer can include an optical barcode scanner. In the latter case it can include an RFID reader.

The printer may also be capable of rendering the item ID in other forms.For example, it may be capable of printing the item ID in the form of a2D bar code, or of printing the product ID component of the item ID inthe form of a ID bar code, or of writing the item ID to a writable orwrite-once RFID tag.

4.4 Omnitag Scanning

Item information typically flows to the product server in response tosituated scan events, e.g. when an item is scanned into inventory ondelivery; when the item is placed on a retail shelf; and when the itemis scanned at point of sale. Both fixed and hand-held scanners may beused to scan omnitagged product items, using both laser-based 2Dscanning and 2D image-sensor-based scanning, using similar or the sametechniques as employed in the netpage pen.

As shown in FIG. 16, both a fixed scanner 254 and a hand-held scanner252 communicate scan data to the product server 251. The product servermay in turn communicate product item event data to a peer product server(not shown), or to a product application server 250, which may implementsharing of data with related product servers. For example, stockmovements within a retail store may be recorded locally on the retailstore's product server, but the manufacturer's product server may benotified once a product item is sold.

4.5 Omnitag-Based Netpage Interactions

A product item whose labelling, packaging or actual surface has beenomnitagged provides the same level of interactivity as any othernetpage.

There is a strong case to be made for netpage-compatible producttagging. Netpage turns any printed surface into a finely differentiatedgraphical user interface akin to a Web page, and there are manyapplications which map nicely onto the surface of a product. Theseapplications include obtaining product information of various kinds(nutritional information; cooking instructions; recipes; relatedproducts; use-by dates; servicing instructions; recall notices); playinggames; entering competitions; managing ownership (registration; query,such as in the case of stolen goods; transfer); providing productfeedback; messaging; and indirect device control. If, on the other hand,the product tagging is undifferentiated, such as in the case of anundifferentiated 2D barcode or RFID-carried item ID, then the burden ofinformation navigation is transferred to the information deliverydevice, which may significantly increase the complexity of the userexperience or the required sophistication of the delivery device userinterface.

The invention will now be described with reference to the followingexamples. However, it will of course be appreciated that this inventionmay be embodied in many other forms without departing from the scope ofthe invention, as defined in the accompanying claims.

EXAMPLES

In the following examples, uv-visible spectra are reportedconventionally by stating an absorption wavelength first, followed bythe corresponding log ε_(max) in parentheses. For example, “760 (5.11)”denotes an absorption at 760 nm having a log ε_(max) of 5.11.

Example 1

(a) Metal Free Phthalocyanine—H₂Pc(dib)₄(OBu)₈

Lithium metal (78.2 mg; 11 mmol) was added portionwise to a boilingsolution of the phthalonitrile (203 mg; 0.49 mmol) in n-butanol (10 mL).After 45 min the reaction mixture was cooled, and diluted with water (20mL) and acetic acid (5 mL). The dark mixture was poured into water (200mL) and extracted with chloroform (3×150 mL). The combined extracts weredried (Na₂SO₄) and the solvents were removed under high vacuum. Thecrude phthalocyanine was purified by column chromatography [alumina(activity grade I), toluene] to give the pure product as an apple-greenpowder (90 mg; 47%). λ_(max) 760 (5.11), 732 (5.07), 693 (4.54), 660(4.48), 402 (4.61), 331 (4.62); ¹H NMR spectrum (CDCl₃) δ −0.20 (2H, s,NH), 1.16 (24H, t, J=7.3 Hz, 8×CH₃), 1.69 (16H, sxt, J=7.3 Hz, 8×CH₂),2.20 (16H, qnt, J=7.3 Hz, 8×CH₂), 4.93 (16H, t, J=7.3 Hz, 8×CH₂O), 6.50(8H, s, 8×CH), 7.10-7.13 (16H, m, Ar—H), 7.63-7.65 (16H, m, Ar—H).

Example 2

(b) Vanadyl Octabutoxyphthalocyanine

H₂Pc(dib)₄(OBu)₈ (113 mg; 0.071 mmol) was suspended in dry DMF (5 mL)and then vanadyl acetylacetonate (97 mg; 0.37 mmol) and tributylamine(500 μL) were added consecutively with stirring. The resulting mixturewas heated under reflux overnight, cooled and diluted withdichloromethane (200 mL). The solution was washed with water (100 mL),HCl (0.1 M; 2×100 mL) and saturated NaHCO₃ (100 mL), and dried (MgSO₄).Removal of the solvent left a dark green solid that was dissolved intoluene and purified by column chromatography on neutral alumina(toluene). The first green band contained the product and removal of thesolvent afforded a green powder (90 mg; 76%). ¹H NMR (CDCl₃) (allsignals are broad) δ1.15-1.26; 1.67-1.76; 2.1-2.4; 4.9-5.0; 6.4-6.7;7.10-7.23; 7.64-7.70; λ_(max) 768 (5.2), 688 (4.6), 401 (4.6), 357(4.6), 331 (4.7) nm.

Example 3

(c) Sulfonation of VOPc(dib)₄(OBu)₈S₈ to VOPc(dib)₄(OBu)₈S₈

VOPc(dib)₄(OBu)_(g) (22.7 mg; 13.7 μmol) in oleum (1.5 mL) was stirredat room temperature for 1 h. The deep blue solution containing thesulfonated derivative (presumed to be VOPc(dib)₄(OBu)₈S₈) was firstanalysed by taking an aliquot and diluting it in DMSO to give a 10 μMsolution. The resulting purple solution had λ_(max) 843, 746 nm. Theremainder of the reaction solution was quenched by carefully adding itto ice (5 g) and washing with sulfuric acid (98%, 0.5 mL) giving a totalvolume of 6 mL. Aliquots (4×1 mL) of this solution were diluted to 5 mLwith either water (2× samples) or ink-base (2× samples). One of eachpair of samples was neutralised with solid NaHCO₃ to pH 7-8 while theother samples remained acidic (Table 1). The final concentration of eachsample was ca. 4 mg in 5 mL (ca. 0.1% w/v). Each solution was applied toplain paper (80 gsm) with a brush and reflectance spectra were recordedon a Cary SE spectrometer with an integrating sphere. TABLE 1Composition of ink-base ingredient Concentration (v/v) Polyethyleneglycol 400 9.0% 1,2-hexanediol 6.0% glycerol 6.0% triethylene glycolmonomethyl ether 2.0% triethylene glycol 1.0% Surfynol ® surfactant 0.5%0.01 M acetic acid 74.5%

TABLE 2 Test solutions for reflectance vis-NIR spectroscopy samplemedium additive pH 1 Water None <2 2 Water NaHCO₃ 7-8 3 Ink-base None <24 Ink-base NaHCO₃ 7-8

Example 4

Nickel Dithiolene Camphorsulfonic Acid Dipotassium Salt

Phosphorous pentasulfide (12.5 g; 0.028 mol) was added to a solution ofcamphorquinonesulfonic acid mono-hydrate (5.1 g; 0.019 mol) in freshlydistilled dioxane (150 mL). The resulting mixture was heated underreflux for 2 h under a nitrogen atmosphere. After this time the reactionmixture was cooled slightly and while still quite warm was filteredthrough a sintered glass funnel to remove unreacted P₄S₁₀. Nickelchloride hexahydrate (8.2 g; 0.034 mol) in water (100 mL) was added tothe filtrate and the resulting mixture was heated under reflux for afurther 2 h. During this time the colour changed from green/beige toblack. The reaction mixture was consecutively cooled, diluted with water(200 mL), treated with tetrabutylammonium hydroxide (40%, 50 mL) andextracted with dichloromethane (3×250 mL). The dichloromethane wasremoved by evaporation and the residue was dissolved in ethanol (500mL). The ethanol solution was percolated through a sintered glass funnelcontaining DOWEX-H⁺ resin, washing with more ethanol, in order toconvert the tetrabutylammonium salt into the free acid. The blackethanol solution was treated with potassium tert-butoxide (2 g; 0.018mol) in ethanol (50 mL) with stirring. The resulting cloudy brownmixture was filtered, washing consecutively with ethanol, warm ethanol,warm ether, and finally warm acetone to give the nickel dithiolenedipotassium salt as a dark purple solid (3.14 g; 44%). λ_(max) 781(4.11), 541 (2.95); MS (ESI) m/z: 651 [(M-K)⁻, 27%), 306 [(M−2K)²⁻,100]; HRMS: m/z calcd for C₂₀H₂₆NiO₆S₆ ²⁻ (M⁺−2K)²⁻ 305.9708, found305.9711.

Example 5

Nickel Dithiolene Camphorsulfonic Acid Disodium Salt

A mixture of camphorquinonesulfonic acid mono-hydrate (4.12 g, 0.016mol) and phosphorous pentasulfide (10.3 g, 0.023 mol) in dioxane (100mL) was heated at reflux for 2 h. The excess phosphorous pentasulfidewas filtered off and washed with dioxane (50 mL). A solution of nickel(II) chloride hexahydrate (8.10 g, 0.034 mol) in water (50 mL) was addedto the dioxane solution and the black reaction mixture heated at refluxfor 2 h. The resulting dark-magenta solution was diluted with water (500mL), filtered and extracted with chloroform (2×200 mL). The aqueouslayer was basified to pH 8 with tetrabutylammonium hydroxide (40%, 60mL) and extracted with chloroform (3×200 mL). The combined organiclayers were washed with water (1×200 mL) and the solvent removed underreduced pressure. The tetrabutylammonium salt was dissolved in ethanoland eluted through a column of DOWEX-H⁺ resin to give the free acid.This ethanol solution was then eluted through a column of AmberliteIRP-64 resin (Na⁺ form) and the solvent removed to give the sodium saltas a dark-purple powder. λ_(max) 783 nm; (ESI) m/z: 635 [(M−Na)⁻, 27%),306 [(M−2Na)²⁻, 100]; HRMS: m/z calcd for C₂₀H₂₆NiO₆S₆ ²⁻ (M⁺−2Na)²⁻305.9708, found 305.9723.

Example 6

Palladium Dithiolene Camphorsulfonic Acid Dipotassium Salt

Phosphorous pentasulfide (1.97 g; 4.4 mmol) was added to a solution ofcamphorquinonesulfonic acid mono-hydrate (0.59 g; 2.2 mmol) in freshlydistilled dioxane (30 mL). The reaction mixture was heated under refluxfor 2 h and filtered. The filtrate was treated with palladium acetate(0.25 g; 1.1 mmol) in water (10 mL) with stirring causing the reactionmixture to become cloudy and then dark purple in colour. The whole washeated under reflux for 2 h and diluted with water (300 mL).Tetrabutylammonium hydroxide solution (40%, 5 mL) was added and then themixture was extracted with chloroform (3×100 mL). The solvent wasremoved by evaporation and the purple residue was dissolved in ethanol(50 mL) before percolating through a DOWEX-H⁺ column. The DOWEX waswashed with ethanol until colourless (150 mL). The resulting ethanolsolution was treated with potassium t-butoxide (1 g; 8.9 mmol) andcooled causing a purple solid to separate out. The solid was filtered,washed with ethanol (100 mL), and dried thereby affording the palladiumcomplex as a purple solid (0.382 g; 50%). λ_(max) 831 nm.

1. A method of minimizing absorption of visible light in an IR-absorbingdye comprising reducing intermolecular interactions between adjacent dyemolecules.
 2. The method of claim 1, wherein the dye comprises asubstantially planar π-system and the intermolecular interaction are π-πinteractions.
 3. The method of claim 1, wherein the intermolecularinteractions are reduced by steric repulsion.
 4. The method of claim 2,wherein the dye molecule comprises at least one moiety, which extendsout of the plane of the substantially planar π-system.
 5. The method ofclaim 1, wherein the intermolecular interactions are reduced using abridged cyclic group.
 6. The method of claim 1, wherein theintermolecular interactions are reduced using a polymeric group.
 7. Themethod of claim 6, wherein the polymeric group is a dendrimer.
 8. Themethod of claim 6, wherein the polymeric group includes a PEG chain. 9.The method of claim 1, wherein the IR-absorbing dye is a metal-liganddye.
 10. The method of claim 9, wherein the IR-absorbing dye is ametal-cyanine dye.
 11. The method of claim 9, wherein the IR-absorbingdye is a metal-dithiolene dye.
 12. The method of claim 9 comprisingpreselecting a metal-ligand dye, wherein at least one ligand includes abridged cyclic group.
 13. The method of claim 9 comprising preselectinga metal-ligand dye, wherein at least one ligand includes a polymericgroup.
 14. The method of claim 9 comprising preselecting a metal-liganddye, wherein at least one ligand includes a dendrimer.
 15. The method ofclaim 9 comprising preselecting a metal-ligand dye, wherein at least oneligand includes a PEG chain.
 16. A method of minimizing absorption ofvisible light in an inkjet ink comprising an IR-absorbing dye, saidmethod comprising reducing intermolecular interactions between adjacentdye molecules.
 17. The method of claim 16, wherein said inkjet inkfurther comprises a singlet oxygen quencher.
 18. The method of claim 16,wherein said inkjet ink is contained in an ink reservoir in fluidcommunication with a printhead of an inkjet printer.
 19. The method ofclaim 18, wherein said wherein said printhead comprises: a plurality ofnozzles; a bubble forming chamber corresponding to each of the nozzlesrespectively, the bubble forming chambers adapted to contain ejectableliquid; and a heater element disposed in each of the bubble formingchambers respectively, the heater element configured for thermal contactwith the ejectable liquid; such that, heating the heater element to atemperature above the boiling point of the ejectable liquid forms a gasbubble that causes the ejection of a drop of the ejectable liquid fromthe nozzle; wherein, the heater element is suspended in the ink chambersuch that during use at least a portion of the heater element isencircled by, and in direct contact with, the ejectable fluid.
 20. Themethod of claim 16, wherein said inkjet ink is contained in an inkcartridge.
 21. A method of minimizing visible coloration of a substratehaving an IR-absorbing dye disposed thereon, said method comprisingreducing intermolecular interactions between adjacent dye molecules. 22.The method of claim 21, wherein said dye is disposed in the form ofcoded data.
 23. The method of claim 22, wherein said substrate comprisesan interface surface and wherein the coded data is disposed over asubstantial portion of said interface surface.
 24. The method claim 21,wherein said substrate is a paper sheet, a label, a tag, a packagingmaterial or a product item.
 25. A method of enabling entry of data intoa computer system via a printed form, the form containing human-readableinformation and machine-readable coded data, the coded data beingindicative of an identity of the form and of a plurality of referencepoints of the form, the method including the steps of: receiving, in thecomputer system and from a sensing device, indicating data regarding theidentity of the form and a position of the sensing device relative tothe form, the sensing device, when placed in an operative positionrelative to the form, generating the indicating data using at least someof the coded data; identifying, in the computer system and from theindicating data, at least one field of the form; and interpreting, inthe computer system, at least some of the indicating data as it relatesto the at least one field, wherein said coded data comprises anIR-absorbing dye in which visible absorption is minimized by a methodaccording to claim
 1. 26. The method of claim 25 in which the at leastone field is associated with at least one zone of the form, theidentifying step including identifying that the position of the sensingdevice is within the at least one zone.
 27. The method of claim 26 inwhich the indicating data includes movement data regarding movement ofthe sensing device relative to the form, the sensing device generatingthe movement data using at least some of the coded data, the identifyingstep including identifying that the movement of the sensing device is atleast partially within the at least one zone.
 28. A method of enablingentry of data into a computer system via a printed form, the formcontaining human-readable information and machine-readable coded data,the coded data being indicative of at least one field of the form, themethod including the steps of: receiving, in the computer system andfrom a sensing device, indicating data regarding the at least one fieldand including movement data regarding movement of the sensing devicerelative to the form, the sensing device, when moved relative to theform, generating the data regarding said at least one field using atleast some of the coded data and generating the data regarding its ownmovement relative to the form; and interpreting, in the computer system,at least some of said indicating data as it relates to said at least onefield, wherein said coded data comprises an IR-absorbing dye in whichvisible absorption is minimized by a method according to claim
 1. 29.The method of claim 28 in which the sensing device generates themovement data using at least some of the coded data.
 30. The method anyone of claims 26, 27 and 28 in which the at least one field is a textfield and the interpreting step includes converting at least some of themovement data to text.
 31. The method any one of claims 26, 27 and 28 inwhich the at least one field is a drawing field.
 32. The method any oneof claims 26, 27 and 28 in which the at least one field is a checkboxfield and the interpreting step includes interpreting at least some ofthe movement data as a check mark.
 33. The method any one of claims 26,27 and 28 in which the at least one field is a signature field and theinterpreting step includes verifying that at least some of the movementdata represents a signature of a user associated with the sensingdevice.
 34. The method of claim 25 or claim 28 in which the at least onefield is an action field and the interpreting step includes sending amessage to an application associated with the action field.
 35. Themethod of claim 34 in which the action field is a form submission actionfield and the message includes form data derived from at least one otherfield of the form.
 36. A method of enabling entry of data into acomputer system via a product item, the product item having a printedsurface containing human-readable information and machine-readable codeddata, the coded data being indicative of an identity of the productitem, the method including the steps of: (a) receiving, in the computersystem and from a sensing device, indicating data regarding the identityof the product item, the sensing device, when placed in an operativeposition relative to the product item, generating the indicating datausing at least some of the coded data; and (b) recording, in thecomputer system and using the indicating data, information relating tothe product item, wherein said coded data comprises an IR-absorbing dyein which visible absorption is minimized by a method according toclaim
 1. 37. A method of enabling retrieval of data from a computersystem via a product item, the product item having a printed surfacecontaining human-readable information and machine-readable coded data,the coded data being indicative of an identity of the product item, themethod including the steps of: (a) receiving, in the computer system andfrom a sensing device, indicating data regarding the identity of theproduct item, the sensing device, when placed in an operative positionrelative to the product item, generating the indicating data using atleast some of the coded data; (b) retrieving, in the computer system andusing the indicating data, information relating to the product item; and(c) outputting, from the computer system and to an output device, theinformation relating to the product item, the output device selectedfrom the group comprising a display device and a printing device,wherein said coded data comprises an IR-absorbing dye in which visibleabsorption is minimized by a method according to claim
 1. 38. The methodof claim 36 or 37 in which the coded data is formed from a plurality ofcoded data portions, each coded data portion being indicative of theidentity of the product item.
 39. The method of claim 36 or 37 in whichthe coded data is indicative of at least one of a UPC and an EPCassociated with the product item.
 40. The method of claim 25 or 28 inwhich the form is disposed on a surface of a product item and in whichthe coded data is indicative of an identity of the product item.
 41. Themethod of claim 40 in which the coded data is formed from a plurality ofcoded data portions, each coded data portion being indicative of theidentity of the product item.
 42. The method of claim 40 in which thecoded data is indicative of at least one of a UPC and an EPC associatedwith the product item.
 43. The method of any one of claims 25, 28, 36 or37 in which the coded data is substantially invisible to an unaidedhuman eye.